Disseminated mycobacterial infection was found at autopsy in a male patient with hemophilia B and acquired immunodeficiency syndrome (AIDS). In May 1986, 23 months before death, the patient had encephalitis for one month and in July he developed a fever, malaise and generalized lymphoadenopathy. Human immunosuppressive virus (HIV) was positive and the CD 4/8 ratio of lymphocyte surface markers was 0.1, but mycobacterium was not detected. In September 1986, he had severe dyspnea due to interstitial pneumonia and he was treated with high-dose methylprednisolone. He died after a 23-month course of fever, severe weight loss and terminal progressive deterioration, although he was treated with antibiotics, antifungal agents, gamma-globulin, steroid and a Azidothymidine.