diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index e70339ae1271f..7a8f905a9d245 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -4470,5 +4470,9 @@
     "Add all missing enum members": {
         "category": "Message",
         "code": 95064
+    },
+    "Private names are not allowed outside of class bodies": {
+        "category": "Error",
+        "code": 95065
     }
 }
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index bfc502ce2da1e..7a27b626fd152 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -1320,15 +1320,22 @@ namespace ts {
         // An identifier that starts with two underscores has an extra underscore character prepended to it to avoid issues
         // with magic property names like '__proto__'. The 'identifiers' object is used to share a single string instance for
         // each identifier in order to reduce memory consumption.
-        function createIdentifier(isIdentifier: boolean, diagnosticMessage?: DiagnosticMessage): Identifier {
+        function createIdentifier(isIdentifier: boolean, suggestedDiagnosticMessage?: DiagnosticMessage): Identifier {
             identifierCount++;
-            if (isIdentifier) {
+            let diagnosticMessage = suggestedDiagnosticMessage;
+            const isPrivateName = !!(scanner.getTokenFlags() & TokenFlags.PrivateName);
+            const privateNameIsAllowed = !!(parsingContext & (1 << ParsingContext.ClassMembers));
+            if (isPrivateName && !privateNameIsAllowed) {
+                diagnosticMessage = Diagnostics.Private_names_are_not_allowed_outside_of_class_bodies;
+            }
+            else if (isIdentifier && (!isPrivateName || privateNameIsAllowed)) {
                 const node = <Identifier>createNode(SyntaxKind.Identifier);
 
                 // Store original token kind if it is not just an Identifier so we can report appropriate error later in type checker
                 if (token() !== SyntaxKind.Identifier) {
                     node.originalKeywordKind = token();
                 }
+                node.isPrivateName = isPrivateName;
                 node.escapedText = escapeLeadingUnderscores(internIdentifier(scanner.getTokenValue()));
                 nextToken();
                 return finishNode(node);
diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index af74d69ceefbb..5df5a2a66902e 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -1723,6 +1723,21 @@ namespace ts {
                         error(Diagnostics.Invalid_character);
                         pos++;
                         return token = SyntaxKind.Unknown;
+                    case CharacterCodes.hash:
+                        pos++;
+                        if (isIdentifierStart(ch = text.charCodeAt(pos), languageVersion)) {
+                            tokenFlags |= TokenFlags.PrivateName;
+                            pos++;
+                            while (pos < end && isIdentifierPart(ch = text.charCodeAt(pos), languageVersion)) pos++;
+                            tokenValue = text.substring(tokenPos, pos);
+                            if (ch === CharacterCodes.backslash) {
+                                tokenValue += scanIdentifierParts();
+                            }
+                            return token = SyntaxKind.Identifier;
+                        }
+                        error(Diagnostics.Invalid_character);
+                        // no `pos++` because already advanced at beginning of this `case` statement
+                        return token = SyntaxKind.Unknown;
                     default:
                         if (isIdentifierStart(ch, languageVersion)) {
                             pos++;
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 85efeb96ea5d7..ff8257ddd3962 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -683,6 +683,7 @@ namespace ts {
          */
         escapedText: __String;
         originalKeywordKind?: SyntaxKind;                         // Original syntaxKind which get set so that we can report an error later
+        isPrivateName: boolean;                                   // is private name like `this.#foo`
         /*@internal*/ autoGenerateFlags?: GeneratedIdentifierFlags; // Specifies whether to auto-generate the text for an identifier.
         /*@internal*/ autoGenerateId?: number;                    // Ensures unique generated identifiers get unique names, but clones get the same name.
         isInJSDocNamespace?: boolean;                             // if the node is a member in a JSDoc namespace
@@ -1574,6 +1575,7 @@ namespace ts {
         BinarySpecifier = 1 << 7,   // e.g. `0b0110010000000000`
         OctalSpecifier = 1 << 8,    // e.g. `0o777`
         ContainsSeparator = 1 << 9, // e.g. `0b1100_0101`
+        PrivateName = 1 << 10,      // e.g. `#foo`
         BinaryOrOctalSpecifier = BinarySpecifier | OctalSpecifier,
         NumericLiteralFlags = Scientific | Octal | HexSpecifier | BinarySpecifier | OctalSpecifier | ContainsSeparator
     }
diff --git a/src/services/services.ts b/src/services/services.ts
index b2a2fdaaae21e..b9771e977ffac 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -347,6 +347,7 @@ namespace ts {
         public kind: SyntaxKind.Identifier;
         public escapedText: __String;
         public symbol: Symbol;
+        public isPrivateName: boolean;
         public autoGenerateFlags: GeneratedIdentifierFlags;
         _primaryExpressionBrand: any;
         _memberExpressionBrand: any;