Background. Respiratory illness is a significant contributor to morbidity and mortality in patients with human immunodeficiency virus (HIV) infection and the acquired immuodeficiency syndrome (AIDS). It has been suggested that Pneumocystis carinii pneumonia is no longer the most frequent cause of respiratory disease in this group because of widespread use of prophylaxis and anti-retroviral drugs. Methods. A retrospective comparison of the diagnoses in HIV 1 antibody positive patients with respiratory illness admitted to a major UK centre in 1986-7 and 1990-1 was carried out to identify changes in patterns of respiratory disease. Results. In the 1986-7 period there were 73 patients, of whom none received zidovudine or prophylaxis for pneumocystis pneumonia while in the 1990-1 period there were 122 patients. One hundred and ninety patients (98%) were male homosexuals. Pneumocystis pneumonia remained the commonest respiratory disease, comprising 68% of all diagnoses in the 1986-7 period and 48% in the 1990-1 period. Bacterial infections (Bronchitis and pneumonia) were seen more commonly in the 1990-1 period (23%) than in the 1986-7 period (14%), as was pulmonary Kaposi's sarcoma (12% in 1990-1 and 4% in 1986-7). Mycobacterial infection remained uncommon (4% in 1986-7 and 6.5% in 1990-1). Conclusion. Despite widespread use of zidovudine and prophylaxis, pneumocystis pneumonia remains the commonest respiratory disease in homosexual men.