diff --git a/solidity/underscore-prefix-function.sol b/solidity/underscore-prefix-function.sol
new file mode 100644
index 0000000..b27b9b8
--- /dev/null
+++ b/solidity/underscore-prefix-function.sol
@@ -0,0 +1,17 @@
+contract Test {
+	// ok: underscore-prefix-function
+	function _smth() internal {
+		//
+	}
+
+	// ruleid: underscore-prefix-function
+	function _not_Internal(bytes opa) public {
+		uint256 a = 1;
+	}
+
+	// ok: underscore-prefix-function
+	function _smth(string lulz) private {
+		uint256 a = 1;
+	}
+
+}
\ No newline at end of file
diff --git a/solidity/underscore-prefix-function.yaml b/solidity/underscore-prefix-function.yaml
new file mode 100644
index 0000000..e76052c
--- /dev/null
+++ b/solidity/underscore-prefix-function.yaml
@@ -0,0 +1,22 @@
+rules:
+  - id: underscore-prefix-function
+    message: The convention of functions named with the "_" prefix is not clear. Sometimes it is used for internal functions and other times it's not
+    languages:
+      - solidity
+    severity: WARNING
+    metadata:
+      category: coding-style
+      tags:
+        - compound
+      references:
+        - https://github.com/compound-finance/comet/issues/396
+    patterns:
+      - metavariable-regex:
+          metavariable: $FUNC
+          regex: "^_"
+      - pattern: |
+          function $FUNC(...) { ... }
+      - pattern-not: |
+          function $FUNC(...) internal { ... }
+      - pattern-not: |
+          function $FUNC(...) private { ... }