The prevalence of AIDS in Mexico and the frequency of sexually transmitted risks was analyzed in relation to the socioeconomic strata of the patients. The study was based on the obligatory notifications of AIDS received by the Ministry of Health between 1982 and september of 1988. The findings show that AIDS is accumulating more rapidly among the low socioeconomic strata, where the bisexual and heterosexual risk factors are also more frequent. These findings are explained in the context of the sexual mores and living conditions of the low social strata of the country. The study leads to the recommendation of diversified preventive activities that meet the peculiarities of the various social strata in Mexico.