diff --git a/contracts/base/SemaphoreGroups.sol b/contracts/base/SemaphoreGroups.sol
index 61bad826d..df9154477 100644
--- a/contracts/base/SemaphoreGroups.sol
+++ b/contracts/base/SemaphoreGroups.sol
@@ -48,8 +48,9 @@ abstract contract SemaphoreGroups is Context, ISemaphoreGroups {
         groups[groupId].insert(identityCommitment);
 
         uint256 merkleTreeRoot = getMerkleTreeRoot(groupId);
+        uint256 index = getNumberOfMerkleTreeLeaves(groupId) - 1;
 
-        emit MemberAdded(groupId, identityCommitment, merkleTreeRoot);
+        emit MemberAdded(groupId, index, identityCommitment, merkleTreeRoot);
     }
 
     /// @dev Updates an identity commitment of an existing group. A proof of membership is
@@ -73,8 +74,9 @@ abstract contract SemaphoreGroups is Context, ISemaphoreGroups {
         groups[groupId].update(identityCommitment, newIdentityCommitment, proofSiblings, proofPathIndices);
 
         uint256 merkleTreeRoot = getMerkleTreeRoot(groupId);
+        uint256 index = proofPathIndicesToMemberIndex(proofPathIndices);
 
-        emit MemberUpdated(groupId, identityCommitment, newIdentityCommitment, merkleTreeRoot);
+        emit MemberUpdated(groupId, index, identityCommitment, newIdentityCommitment, merkleTreeRoot);
     }
 
     /// @dev Removes an identity commitment from an existing group. A proof of membership is
@@ -96,8 +98,9 @@ abstract contract SemaphoreGroups is Context, ISemaphoreGroups {
         groups[groupId].remove(identityCommitment, proofSiblings, proofPathIndices);
 
         uint256 merkleTreeRoot = getMerkleTreeRoot(groupId);
+        uint256 index = proofPathIndicesToMemberIndex(proofPathIndices);
 
-        emit MemberRemoved(groupId, identityCommitment, merkleTreeRoot);
+        emit MemberRemoved(groupId, index, identityCommitment, merkleTreeRoot);
     }
 
     /// @dev See {ISemaphoreGroups-getMerkleTreeRoot}.
@@ -114,4 +117,27 @@ abstract contract SemaphoreGroups is Context, ISemaphoreGroups {
     function getNumberOfMerkleTreeLeaves(uint256 groupId) public view virtual override returns (uint256) {
         return groups[groupId].numberOfLeaves;
     }
+
+    /// @dev Converts the path indices of a Merkle proof to the identity commitment index in the tree.
+    /// @param proofPathIndices: Path of the proof of membership.
+    /// @return Index of a group member.
+    function proofPathIndicesToMemberIndex(uint8[] calldata proofPathIndices) private pure returns (uint256) {
+        uint256 memberIndex = 0;
+
+        for (uint8 i = uint8(proofPathIndices.length); i > 0; ) {
+            if (memberIndex > 0 || proofPathIndices[i - 1] != 0) {
+                memberIndex *= 2;
+
+                if (proofPathIndices[i - 1] == 1) {
+                    memberIndex += 1;
+                }
+            }
+
+            unchecked {
+                --i;
+            }
+        }
+
+        return memberIndex;
+    }
 }
diff --git a/contracts/interfaces/ISemaphoreGroups.sol b/contracts/interfaces/ISemaphoreGroups.sol
index 346358fcb..797d4e5a0 100644
--- a/contracts/interfaces/ISemaphoreGroups.sol
+++ b/contracts/interfaces/ISemaphoreGroups.sol
@@ -16,17 +16,20 @@ interface ISemaphoreGroups {
 
     /// @dev Emitted when a new identity commitment is added.
     /// @param groupId: Group id of the group.
+    /// @param index: Identity commitment index.
     /// @param identityCommitment: New identity commitment.
     /// @param merkleTreeRoot: New root hash of the tree.
-    event MemberAdded(uint256 indexed groupId, uint256 identityCommitment, uint256 merkleTreeRoot);
+    event MemberAdded(uint256 indexed groupId, uint256 index, uint256 identityCommitment, uint256 merkleTreeRoot);
 
     /// @dev Emitted when an identity commitment is updated.
     /// @param groupId: Group id of the group.
-    /// @param identityCommitment: New identity commitment.
+    /// @param index: Identity commitment index.
+    /// @param identityCommitment: Existing identity commitment to be updated.
     /// @param newIdentityCommitment: New identity commitment.
     /// @param merkleTreeRoot: New root hash of the tree.
     event MemberUpdated(
         uint256 indexed groupId,
+        uint256 index,
         uint256 identityCommitment,
         uint256 newIdentityCommitment,
         uint256 merkleTreeRoot
@@ -34,9 +37,10 @@ interface ISemaphoreGroups {
 
     /// @dev Emitted when a new identity commitment is removed.
     /// @param groupId: Group id of the group.
+    /// @param index: Identity commitment index.
     /// @param identityCommitment: Existing identity commitment to be removed.
     /// @param merkleTreeRoot: New root hash of the tree.
-    event MemberRemoved(uint256 indexed groupId, uint256 identityCommitment, uint256 merkleTreeRoot);
+    event MemberRemoved(uint256 indexed groupId, uint256 index, uint256 identityCommitment, uint256 merkleTreeRoot);
 
     /// @dev Returns the last root hash of a group.
     /// @param groupId: Id of the group.
diff --git a/test/Semaphore.ts b/test/Semaphore.ts
index 969dd1460..2fef9c47f 100644
--- a/test/Semaphore.ts
+++ b/test/Semaphore.ts
@@ -101,6 +101,7 @@ describe("Semaphore", () => {
                 .to.emit(contract, "MemberAdded")
                 .withArgs(
                     groupId,
+                    0,
                     members[0],
                     "18951329906296061785889394467312334959162736293275411745101070722914184798221"
                 )
@@ -125,7 +126,7 @@ describe("Semaphore", () => {
 
             const transaction = contract.addMembers(groupId, members)
 
-            await expect(transaction).to.emit(contract, "MemberAdded").withArgs(groupId, BigInt(3), group.root)
+            await expect(transaction).to.emit(contract, "MemberAdded").withArgs(groupId, 2, BigInt(3), group.root)
         })
     })
 
@@ -152,7 +153,9 @@ describe("Semaphore", () => {
 
             const transaction = contract.updateMember(groupId, BigInt(1), BigInt(4), siblings, pathIndices)
 
-            await expect(transaction).to.emit(contract, "MemberUpdated").withArgs(groupId, BigInt(1), BigInt(4), root)
+            await expect(transaction)
+                .to.emit(contract, "MemberUpdated")
+                .withArgs(groupId, 0, BigInt(1), BigInt(4), root)
         })
     })
 
@@ -170,16 +173,16 @@ describe("Semaphore", () => {
 
             group.addMembers(members)
 
-            group.removeMember(0)
+            group.removeMember(2)
 
             await contract["createGroup(uint256,uint256,uint256,address)"](groupId, treeDepth, 0, accounts[0])
             await contract.addMembers(groupId, members)
 
-            const { siblings, pathIndices, root } = group.generateProofOfMembership(0)
+            const { siblings, pathIndices, root } = group.generateProofOfMembership(2)
 
-            const transaction = contract.removeMember(groupId, BigInt(1), siblings, pathIndices)
+            const transaction = contract.removeMember(groupId, BigInt(3), siblings, pathIndices)
 
-            await expect(transaction).to.emit(contract, "MemberRemoved").withArgs(groupId, BigInt(1), root)
+            await expect(transaction).to.emit(contract, "MemberRemoved").withArgs(groupId, 2, BigInt(3), root)
         })
     })
 
diff --git a/test/SemaphoreVoting.ts b/test/SemaphoreVoting.ts
index 73e40cfef..474ed7e95 100644
--- a/test/SemaphoreVoting.ts
+++ b/test/SemaphoreVoting.ts
@@ -120,6 +120,7 @@ describe("SemaphoreVoting", () => {
                 .to.emit(contract, "MemberAdded")
                 .withArgs(
                     pollIds[1],
+                    0,
                     identityCommitment,
                     "14787813191318312920980352979830075893203307366494541177071234930769373297362"
                 )
diff --git a/test/SemaphoreWhistleblowing.ts b/test/SemaphoreWhistleblowing.ts
index b1bd1115a..7a2d0a5a2 100644
--- a/test/SemaphoreWhistleblowing.ts
+++ b/test/SemaphoreWhistleblowing.ts
@@ -85,6 +85,7 @@ describe("SemaphoreWhistleblowing", () => {
                 .to.emit(contract, "MemberAdded")
                 .withArgs(
                     entityIds[0],
+                    0,
                     identityCommitment,
                     "14787813191318312920980352979830075893203307366494541177071234930769373297362"
                 )
@@ -129,6 +130,7 @@ describe("SemaphoreWhistleblowing", () => {
                 .to.emit(contract, "MemberRemoved")
                 .withArgs(
                     entityIds[0],
+                    0,
                     identityCommitment,
                     "15019797232609675441998260052101280400536945603062888308240081994073687793470"
                 )
diff --git a/yarn.lock b/yarn.lock
index 3528084d5..cfd9fda4e 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -6483,7 +6483,7 @@ __metadata:
   dependencies:
     bn.js: ^4.11.8
     ethereumjs-util: ^6.0.0
-  checksum: ae074be0bb012857ab5d3ae644d1163b908a48dd724b7d2567cfde309dc72222d460438f2411936a70dc949dc604ce1ef7118f7273bd525815579143c907e336
+  checksum: 03127d09960e5f8a44167463faf25b2894db2f746376dbb8195b789ed11762f93db9c574eaa7c498c400063508e9dfc1c80de2edf5f0e1406b25c87d860ff2f1
   languageName: node
   linkType: hard