Abstract Eight cases of pinworm infestation of the appendix presenting with symptoms simulating acute appendicitis are reported from a study of 293 appendicectomy operations performed at University College Hospital, London, in the past 2 years. In each case a diagnosis of appendicitis was made on clinical grounds but in 6 patients the appendix was normal histologically. Symptoms mimicking appendicitis but caused by Enterobius vermicularis infestation merit recognition as a disease process and treatment to eradicate the worm must not be overlooked.