diff --git a/src/wp-includes/class-wp-xmlrpc-server.php b/src/wp-includes/class-wp-xmlrpc-server.php
index 7d64d3f46c019..6d83f3fed3799 100644
--- a/src/wp-includes/class-wp-xmlrpc-server.php
+++ b/src/wp-includes/class-wp-xmlrpc-server.php
@@ -3902,6 +3902,7 @@ public function wp_editComment( $args ) {
 	 * Creates a new comment.
 	 *
 	 * @since 2.7.0
+	 * @since 7.2.0 Returns an error if a comment field exceeds its maximum length.
 	 *
 	 * @param array $args {
 	 *     Method arguments. Note: arguments must be ordered as documented.
@@ -4028,6 +4029,12 @@ public function wp_newComment( $args ) {
 			return new IXR_Error( 403, __( 'Comment is required.' ) );
 		}
 
+		$check_max_lengths = wp_check_comment_data_max_lengths( $comment );
+
+		if ( is_wp_error( $check_max_lengths ) ) {
+			return new IXR_Error( 413, __( 'Comment field exceeds maximum length allowed.' ) );
+		}
+
 		/** This action is documented in wp-includes/class-wp-xmlrpc-server.php */
 		do_action( 'xmlrpc_call', 'wp.newComment', $args, $this );
 
diff --git a/tests/phpunit/tests/xmlrpc/wp/newComment.php b/tests/phpunit/tests/xmlrpc/wp/newComment.php
index 00b0617f53839..c1c76e44cf028 100644
--- a/tests/phpunit/tests/xmlrpc/wp/newComment.php
+++ b/tests/phpunit/tests/xmlrpc/wp/newComment.php
@@ -389,4 +389,107 @@ public function data_comments_observe_post_permissions() {
 			),
 		);
 	}
+
+	/**
+	 * Ensure an error is returned when a comment field exceeds its maximum length.
+	 *
+	 * @ticket 38622
+	 *
+	 * @dataProvider data_new_comment_with_field_exceeding_max_length
+	 *
+	 * @param array $content_struct Content struct with one field exceeding its maximum length.
+	 */
+	public function test_new_comment_with_field_exceeding_max_length( $content_struct ) {
+		add_filter( 'xmlrpc_allow_anonymous_comments', '__return_true' );
+
+		$result = $this->myxmlrpcserver->wp_newComment(
+			array(
+				1,
+				'',
+				'',
+				self::$posts['publish']->ID,
+				$content_struct,
+			)
+		);
+
+		$this->assertIXRError( $result );
+		$this->assertSame( 413, $result->code );
+	}
+
+	/**
+	 * Data provider for test_new_comment_with_field_exceeding_max_length.
+	 *
+	 * @return array[]
+	 */
+	public function data_new_comment_with_field_exceeding_max_length() {
+		$defaults = array(
+			'author'       => 'WordPress',
+			'author_email' => 'noreply@wordpress.org',
+			'content'      => 'Test Comment',
+		);
+
+		return array(
+			'author of 246 characters'       => array(
+				array_merge( $defaults, array( 'author' => str_repeat( 'a', 246 ) ) ),
+			),
+			'author email of 101 characters' => array(
+				array_merge( $defaults, array( 'author_email' => str_repeat( 'a', 89 ) . '@example.com' ) ),
+			),
+			'author URL of 201 characters'   => array(
+				array_merge( $defaults, array( 'author_url' => 'https://example.com/' . str_repeat( 'a', 181 ) ) ),
+			),
+			'content of 65526 characters'    => array(
+				array_merge( $defaults, array( 'content' => str_repeat( 'a', 65526 ) ) ),
+			),
+		);
+	}
+
+	/**
+	 * Ensure an error is returned when a logged-in user's comment content exceeds its maximum length.
+	 *
+	 * @ticket 38622
+	 */
+	public function test_new_comment_with_content_exceeding_max_length_logged_in() {
+		$result = $this->myxmlrpcserver->wp_newComment(
+			array(
+				1,
+				'administrator',
+				'administrator',
+				self::$posts['publish']->ID,
+				array(
+					'content' => str_repeat( 'a', 65526 ),
+				),
+			)
+		);
+
+		$this->assertIXRError( $result );
+		$this->assertSame( 413, $result->code );
+	}
+
+	/**
+	 * Ensure a comment with all fields at their maximum length is accepted.
+	 *
+	 * @ticket 38622
+	 */
+	public function test_new_comment_with_fields_at_max_length() {
+		add_filter( 'xmlrpc_allow_anonymous_comments', '__return_true' );
+
+		$result = $this->myxmlrpcserver->wp_newComment(
+			array(
+				1,
+				'',
+				'',
+				self::$posts['publish']->ID,
+				array(
+					'author'       => str_repeat( 'a', 245 ),
+					'author_email' => str_repeat( 'a', 88 ) . '@example.com',
+					'author_url'   => 'https://example.com/' . str_repeat( 'a', 180 ),
+					'content'      => str_repeat( 'a', 65525 ),
+				),
+			)
+		);
+
+		$this->assertNotIXRError( $result );
+		$this->assertIsInt( $result );
+	}
 }