Pneumonia caused by common pyogenic bacteria occurs frequently in HIV-infected patients. Its clinical presentation has been described as being similar to that seen in non-immunosuppressed hosts but clearly different to that of opportunistic pneumonias. An atypical presentation has rarely been seen. In a 10-month period, we saw 12 HIV-infected patients who presented with Haemophilus influenzae pneumonia which was clinically and radiologically indistinguishable from Pneumocystis carinii pneumonia. Ten of the patients were intravenous drug users and were in different stages of HIV disease. The clinical picture was characterized by a prolonged course (median 4 weeks), non-productive cough, dyspnoea, and absence of findings usually present in bacterial pneumonia. Laboratory data frequently showed absence of leukocytosis, increased lactate dehydrogenase levels, hypoxaemia, and decreased CD4+ cell counts. All presented with interstitial or mixed bilateral infiltrates. Resistance to ampicillin and trimethoprim-sulphamethoxazole were each found in seven cases. Eleven patients were cured with antibiotic therapy, although five relapsed. H. influenzae pneumonia should be considered in HIV-infected patients who present with pulmonary symptoms and bilateral infiltrates of subacute or chronic onset. Clinical resolution of pneumonia is the usual outcome, but recurrences of infection are frequent.