The atmosphere of the 5th World Congress on AIDS in Montreal was one of gravity and anticipation. The anticipation was of news of a vaccine, of a therapy to supplement AZT, of clarification of new discoveries, and especially of solutions to the social problems created by AIDS. Information on AIDS and on low-risk sexual practices were the topics of numerous communications among the 6000 presented in the 4 days of the conference. How to adapt treatment to the economic level of countries, given that 1 day of AZT costs the equivalent of a year's income for an African; the economic impact of treatment for seropositive individuals, effects of information programs on condom use, and analysis of discriminatory behavior were other topics. 108,830 cases of AIDS have been reported in the Americas, 24,686 in Africa, 369 in Asia, 21,855 in Europe, and 14,521 in Oceania. The World Health Organization estimates however that in reality there are 450,000 cases of AIDS in the world, not the 157,191 reported. In some urban zones of Africa, 20-30% of adults aged 20-40 years are believed to be infected. The infection is also spreading in Asia. The rate of infection has increased in the past 2 years from 1%-40% among intravenous drug users in Asia and from 1 in 10,000 to 1 in 500 prostitutes in Bangkok. Despite some slow progress in understanding the evolution and treatment of the disease, it remains true that prevention is the best defense against AIDS and should receive priority.