Background - Community acquired bacterial pneumonia is increasingly encountered in HIV infected individuals and some patients have a radiographic lobar pneumonia. Methods - A retrospective review of clinical features, microbiological diagnosis, and outcome of community acquired lobar pneumonia was carried out in HIV positive patients admitted to a specialist unit from 1987 to 1993. Results - Forty nine episodes occurred in 45 patients, all of whom were men. CD4 counts ranged widely. A bacteriological diagnosis was made in 25 episodes (51%), seven patients had more than one infective cause. The commonest pathogens were Streptococcus pneumoniae (11 episodes), Staphylococcus aureus (six), Pneumocystis carinii (three), Haemophilus influenzae (three), and Pseudomonas aeruginosa (two). Four patients died. Other complications included intrapulmonary cavitation or abscess formation (11 episodes), empyema (three), and pleural effusion (10 episodes). Conclusions - Many different infections cause community acquired lobar pneumonia in HIV positive men. Some patients have coinfections and there is a high complication rate.