Lung cavitation in patients with the acquired immune deficiency syndrome (AIDS) and Pneumocystis carinii pneumonia (PCP) has mainly been reported as single case studies. Among 160 episodes of PCP seen in a 1,000 bed teaching hospital and a 600 bed teaching hospital from 1985-1992, we found six cases presenting with lung cavitation and documented Pneumocystis carinii infection. In the cases we report, as well as in the cases reviewed, cavities appear either alone or within an area of pulmonary consolidation, a mass or a nodule. They may present with haemoptysis, show unusual locations, and, most importantly, may frequently be misdiagnosed by bronchoalveolar lavage.