Perforation of the small intestine due to a segmental transmural Pneumocystis carinii infiltrate of the whole circumference was found in a surgical resection specimen as the cause of an acute abdomen in a 48-year-old heterosexual male patient suffering from acquired immunodeficiency syndrome. On autopsy, a disseminated Pneumocystis carinii infection was found involving spleen, thyroid gland and lymph nodes. The origin of this disseminated infection was a recurrent and severe Pneumocystis carinii pneumonia, which was first diagnosed two years before death and was treated with success. The hitherto unknown complication of an extrapulmonary Pneumocystis carinii infection described here extends the spectrum of lethal complications of opportunistic infections in acquired immunodeficiency syndrome.