Pneumocystis carinii pneumonia (PCP) is certainly the most frequent opportunistic pulmonary infection in AIDS patients. Besides the conventional radiographic features demonstrating bilateral infiltrates and airspace consolidation, atypical radiologic patterns are reported in the literature, which are characterized by spontaneous pneumothorax and by the presence of bullae, cysts and areas of pulmonary cavitation. Forty consecutive PCP patients were investigated, ten of them presenting with atypical radiographic findings: 1 case of spontaneous pneumothorax with no evidence of bullae and 9 cases of bullous lung disease--5 of them complicated by spontaneous pneumothorax. Several pathogenetic hypotheses were considered; lesions evolution and the differential radiologic diagnosis were discussed. As for diagnosis, the value of chest CT scans is emphasized, together with that of HRCT which is extremely valuable to localize, characterize and evaluate bullous lesions and associated parenchymal signs.