Acquired immunodeficiency syndrome (AIDS) was first detected in Costa Rica in 1983. For four years most known cases were in hemophiliac men. Thereafter, AIDS in homosexual and bisexual men predominated. By December 31 of 1993, 563 persons had been diagnosed with the syndrome, 71% of them homosexual and bisexual men, 10% heterosexual men and women, 6% hemophiliacs, 2% intravenous drug abusers (IVDA's), 2% women and men who had blood transfusions, 1.4% infants born to HIV-infected mothers and 7% unknown. The epidemics in homosexual/bisexual men and in heterosexual women and men are rising; cases in infants and in persons who received blood or coagulation factors, are stagnant. The steady increase in AIDS among women is linked to exposure to bisexual partners. The moderate nature of the national epidemic reflects, in part, the low incidence of IVDA, the universal screening of blood donors for antibodies to the human immunodeficiency virus (HIV) since 1985, and the prompt banning of unsafe coagulation factors. The projection of AIDS for the year 2000 is 2,304 cases (606 accumulated incidence per million inhabitants). A national educational campaign, radio and television programs and other preventive actions, apparently did not influence the rate of receptive anal intercourse without condom (about 80%) during 9 years of the epidemic. Persons with HIV/AIDS often are deprived of social and medical benefits or are subjected to harassment and exploitation by the health sector. More efficient prevention must target children, adolescents and adults in reproductive age, to promote safer lifestyles, through education and counseling effected through primary health care.