BACKGROUND HIV infection is common in young persons and its clinical picture, outcome and response to antiretroviral therapy is well known, but it is not the case in the elderly. OBJECTIVE To evaluate the clinical characteristics and response to antiretroviral therapy of HIV elderly patients. METHODS Retrospective study of 37 patients elder than 60 years. The control group comprised of 64 HIV positive patients with less than 60 years. None of them were drug abusers. RESULTS The mean age of patients was 65 years (range 60-79), 86% were males. The most frequent causes for HIV testing were: wasting (22%), P. carinii pneumonia (19%), tuberculosis (13%) and Kaposi sarcoma (10%), but in the control group voluntary testing was the most common reason (64%). The mean CD4 count at diagnosis was lower in the elderly group (233 cells/microL vs 323 cells/microL). During follow up, the most frequent complications for those with less than 200 CD4 cells were: oral candidiasis (44%), P. carinii pneumonia (27%), Kaposi sarcoma (22%) and esophageal candidiasis (22%), while in the young group P. carinii pneumonia (22%), Kaposi sarcoma (9%) and esophageal candidiasis (9%) were less frequent. 67% of the elderly received antiretroviral therapy. Zidovudine had to be discontinued due to anaemia in half of them. Survival at 6 and 12 months was significantly longer in treated patients compared to those who did not received antiretrovirals (100% vs 14% at 6 months, P < 0.001; and 54% vs 0% at 12 months, p = 0.03); and at 2 years it was almost similar to that of the young group (36% vs 52%, p = 0.38). CONCLUSIONS HIV infection in the elderly is generally diagnosed in an advance stage, but antiretroviral therapy prolongs survival. Zidovudine should be reserve as a second line drug because its frequent haematological toxicity.