A 33-year-old patient with AIDS, and a history of episodes of Pneumocystis carinii pneumonia and cerebral toxoplasmosis, developed a subcutaneous paravertebral infiltrate, which at first resembled a haematoma. Over a period of several weeks, the lesion spread to cover almost the entire back. Initially, numerous investigations failed to reveal the aetiology. His general condition worsened progressively, and intermittent bleeding into the soft tissue of the back occurred, requiring transfusion. This was associated with the development of an isolated deficiency of clotting factor V and a fall in Quick values to 10%. On the 22nd day after admission, the infiltrate ruptured spontaneously, releasing blood and a large number of whitish spherical masses 2-3 mm in diameter. These were identified as Cysticerci longicolles, the larval form of Taenia crassiceps, a tapeworm occurring in Canidae. The blood clotting values returned to normal within two days of incision of the infiltrate and commencement of therapy with mebendazole (6 g/day) and praziquantel (3.6 g/day). The infiltrate subsequently regressed almost completely. After combination treatment for 2 weeks, treatment was continued with praziquantel alone, which, however, the patient stopped himself after 10 weeks. A recurrence at the same site 4 months later was successfully treated with a further course of mebendazole and praziquantel.