We studied the prevalence of Cryptosporidium in 29 patients with acquired immunodeficiency syndrome (AIDS) from Zulia State, Venezuela. They ranged in age from five months to 46 years. Two were children and 27 were adults, of which six were women. Of the 21 men, 66.6% reported homosexual behavior. Three stool samples from each patient were examined, and modified Ziehl-Neelsen carbolfuchsin staining of formalinether stool concentrates was used to identify Cryptosporidium oocysts. To detect the presence of other intestinal parasites, direct wet mounts and iron-hematoxylin-stained smears were examined. Cryptosporidium was found in 12 (41.3%) of the patients and was identified as a single parasitic infection in seven of the 12 patients (58.3%). Other pathogenic parasites encountered were Giardia lamblia (3 of 12, 25%), Entamoeba histolytica (1 of 12, 8.3%), Ascaris lumbricoides, Trichuris trichiura, and Strongyloides sterocoralis (each 1 of 12, 8.3%). Blastocystis hominis, an organism with an uncertain taxonomic position and pathogenicity, was observed in three of 12 patients (25%). An inflammatory exudate was observed in 10 of 12 patients infected with Cryptosporidium. Most of the patients with this infection presented with chronic watery diarrhea and weight loss. Our results suggest that Cryptosporidium is very common in AIDS patients with diarrhea in Venezuela. However, the role of this parasite as an enteropathogen in these patients is uncertain.