Opportunistic infections (OI's) complicate the outcome of HIV-positive patients. There have been observed regional differences in the incidence and the prevalence of OI's in AIDS patients secondary to immunological deficiencies, environmental factors and socioeconomic and sanitary conditions. At the beginning of the epidemic, the global incidence of OI's in HIV-positive patients was between 60 and 100%. Later, the incidence of tuberculosis, intestinal pathogens, Pneumocystis jiroveci and Mycobacterium avium has decreased in the western hemisphere, because of the pharmacological prophylaxis, the improvement in the medical care and the introduction of the antiretroviral therapy. This phenomenon has been more evident in the United States, in Western Europe, and most Latin American countries. At the beginning of the HIV epidemic, the frequency of the different OI's in Mexico was similar among all the clinical reports; the majority of the cases showed mucocutaneous or esophagic candidiasis, followed by P. jiroveci pneumonia, and Cryptosporidium sp. enteritis. Recently, we have seen an increased in the number of episodes of CMV retinitis and M. avium disseminated infection as evidence of a prolonged survival of the HIV-positive patients. In conclusion, the morbidity and mortality rates in the HIV-positive patients have diminished as a result of the improvement of the medical care, the application of specific OI's prevention measures and more recently to the introduction of HAART.