ObjectivesTo describe epidemiologic patterns and trends in HIV infection in Vietnam from 1996 through 1999, and to summarize the national response to the epidemic.MethodsWe reviewed nationwide HIV case reports, and we analyzed annual seroprevalence among different sentinel populations in 21 provinces, using the &khgr;2test for linear trend to assess trends in HIV prevalence. HIV prevention efforts were also reviewed.ResultsThrough 1999, 17,046 HIV infections, including 2947 AIDS cases and 1523 deaths had been reported in Vietnam. The cumulative incidence rate for the country was 22.5 per 100,000 population. Injection drug users (IDUs) represented 89.0% of all those for whom risk was reported before 1997 and 88.0% in the period 1997 to 1999. In 1999, HIV prevalence rates among IDUs ranged by province from 0% to 89.4%. Significantly increasing HIV trends among IDUs (p< .05) were found in 14 of the 21 sentinel provinces during 1996 to 1999. HIV prevalence among commercial sex workers (CSWs) ranged from 0% to 13.2%, increased significantly in 6 of 21 provinces. In 1999, prevalence among pregnant women, blood donors, and military recruits were 0.12%, 0.20% and 0.61%, respectively. Major prevention activities include mass information; peer education and outreach among groups at increased risk; availability of low-cost syringes and condoms through pharmacies; needle exchange pilot projects; widely available treatment for sexually transmitted diseases; antibody screening of blood for transfusion; and free medical treatment at government hospitals.DiscussionThe HIV epidemic continues to evolve rapidly, intensifying among IDUs and increasing among CSWs. Serosurveillance indicators of HIV in the population at large continue to indicate the relatively slow extension beyond those at highest risk. Immediate, intensive preventions in high-risk groups may decelerate expansion to the broader population.