A study on the prevalence of a common endoparasite in the wild population of the American cockroach was conducted in Penang Island using a trapping method at several sampling sites on the island. Gregarine blattarum was found in the digestive tract in 5 out of 115, or 4.35%, of the wild American cockroaches, Periplaneta americana, that were sampled. This is the first report in Malaysia of Gregarine blattarum in local American cockroaches.