INTRODUCTION: Diarrhea, a common complication and one of the most important causes of malabsorption and malnutrition in AIDS patients. Our objective was to determine the parasitic causes of diarrhea in patients with HIV-AIDS at the Cayetano Heredia National Hospital (Lima, Peru). METHODS: We included 217 HIV-AIDS patients who reported diarrhea between May 2002 and September 2005. We analyzed 1-3 stool samples per patient using six methods to detect oocysts, cysts, eggs and larvae of parasites. RESULTS: The average patients age was 34.5 years (range 15-68); 75.12% were males. Patients with diarrhea during two weeks or more were 149/217 (68.66%). A total of 123 parasites were detected in 103/217 patients (47.5%) 18/217 (8.3%) had mixed parasitic infections. Cryptosporidium spp. was the most frequent parasite detected. It was more prevalent in the group of patients who had diarrhea for two or more weeks than those who had diarrhea for less than two weeks (22.82% vs. 10.29%, p=0.029). Other frequent parasitosis cases were isosporidiasis (10.6%), giardiasis (8.3%) and strongyloidiasis (6.9%). CONCLUSION: Intestinal parasitosis is frequent in HIV-AIDS patients at the Cayetano Heredia National Hospital. The most common opportunistic pathogens were Criptosporidium spp. and Isospora belli and the most frequent non-opportunistic pathogens were Giardia lamblia and Strongyloidiasis stercoralis.