The very rare complication of rectal perforation during the barium enema of an immunocompetent Chinese man with cytomegalovirus (CMV) colitis is described. Rectal biopsy performed over three weeks earlier was unlikely to have been related to the perforation. Histopathological examination of the colonic mucosa showed features of active chronic colitis and CMV infection. After treatment with Ganciclovir, there was cessation of symptoms with eradication of the virus on repeat biopsy samples. It is suggested that presence of CMV colitis predisposed to rectal perforation. The clinical presentation, course of disease and response to treatment supported the concept of CMV as a primary aetiological agent. This complication should be borne in mind when performing barium enemas in patients with clinical features of colitis, especially if they are immunocompromised.