We evaluated the population effectiveness of highly active antiretroviral therapy (HAART) on the risk of AIDS and death in a multicenter cohort of 346 HIV-1 vertically infected children born between 1980 and 2006 in the Comunidad Autónoma de Madrid (CAM), Spain. Risks of AIDS and death in patients with the same duration of HIV infection were compared in different calendar periods [CP1: 1980-1989, CP2: 1990-1993 (reference), CP3: 1994-1996, CP4: 1997-1998, CP5: 1999-2006] through cumulative incidence curves and Cox proportional hazards models, allowing for late entry, that included the calendar period as the time-dependent covariate and adjusting for gender and mother's transmission category. The median follow-up was 11.8 years [interquartile range (IQR), 6.3-15.9]. Median CD4+ T cell percentage increased up to 26.5 in CP5 (IQR, 19.5-36.7) while the viral load decreased (median log(10) copies/ml in CP5, 3.66; IQR, 3.07-4.22). Multivariate analysis showed significant reduction in the risk of death since 1997 onward [CP4: adjusted hazard ratios (AHR), 0.29; 95% confidence interval (CI), 0.12-0.69; CP5: AHR, 0.06; 95% CI, 0.03-0.15]. Reduction in progression to AIDS reached borderline significance in CP4 (AHR, 0.49; 95% CI, 0.23-1.05) and was more marked in the last period (CP5: AHR, 0.30; 95% CI, 0.16-0.59). The reductions in the incidence of AIDS and death observed since 1996 were largely attributable to HAART.