diff --git a/problems/binary-tree-inorder-traversal.kt b/problems/binary-tree-inorder-traversal.kt
new file mode 100644
index 0000000..a1013f3
--- /dev/null
+++ b/problems/binary-tree-inorder-traversal.kt
@@ -0,0 +1,26 @@
+/**
+ * Example:
+ * var ti = TreeNode(5)
+ * var v = ti.`val`
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class Solution {
+    fun inorderTraversal(root: TreeNode?, values: MutableList<Int>): List<Int> {
+        if (root == null) {
+            return values
+        }
+
+        inorderTraversal(root.left, values)
+        values.add(root.`val`!!)
+        inorderTraversal(root.right, values)
+
+        return values
+    }
+
+    fun inorderTraversal(root: TreeNode?): List<Int>
+        = inorderTraversal(root, mutableListOf<Int>())
+}