In a prospective study in AIDS patients with chronic diarrhea, the overall prevalence of intestinal cryptosporidiosis was 15.6% (43/275). The prevalence was higher in homosexual patients (33.3%) than in intravenous drug abusers (10.6%) (p < 0.001). Extraintestinal infection was present in 30% (13/43) of the patients with known intestinal cryptosporidiosis. Eight of the 13 (61.5%) patients with extraintestinal cryptosporidiosis had Cryptosporidium in the bile and 7 of 13 (16.28%) had it in the sputum. Of the seven patients with Cryptosporidium in the sputum, four had respiratory symptoms and an abnormal chest radiograph, although another pulmonary pathogen was isolated simultaneously. Two other patients from whom Cryptosporidium was the sole respiratory pathogen isolated had no respiratory symptoms and normal chest radiographs. The seventh patient had pulmonary symptoms, interstitial infiltrate on chest radiograph and excessive activity on a pulmonary Gallium scan; Cryptosporidium was the only organism detected in induced sputum and bronchoalveolar lavage specimens. The mean CD4+ lymphocyte count in patients with extraintestinal cryptosporidiosis was 55 cells/mm3.