To define age at entry into Tanner stages in children with perinatal HIV-1 infection. Multicentre longitudinal study including 212 perinatally HIV-1-infected children (107 girls and 105 boys) followed-up during puberty (from 8 and 9 years onwards in girls and boys, respectively). Healthy children (843 girls and 821 boys) provided reference percentiles. P2 or B2 stages in girls and P2 or G2 stages in boys defined onset of puberty. The cumulative probability 95% confidence limit (CI) of entry into each stage at different ages was estimated by the Kaplan-Meier product-limit method; differences were evaluated by log rank test. Relationships were tested using the Spearman's rank correlation coefficient. Ages of girls years (95%CI) at P2 12.9 (12.6-13.2), P3 13.4 (13.0-13.8), P4 14.6 (14.0-15.2), B2 12.7 (12.2-13.2), B3 13.3 (12.8-14.0) and B4 14.6 (14.0-15.2) stages were > 97th percentile (> or = 21 month delay) of controls. Ages of boys years (95%CI) at P2 12.6 (12.1-13.1), P3 13.9 (13.4-14.4), P4 14.9 (14.2-15.6), G2 12.1 (11.5-12.7), G3 13.6 (13.1-14.1) and G4 14.9 (14.1-15.7) stages were at the 75-97th percentiles (< or = 15 month delay). Age at onset of puberty was not related to clinical and immunological condition, antiretroviral treatment, weigh for height and age at onset of severe disease or immune suppression. Perinatal HIV-1 infection interferes with sexual maturation. The mechanisms by which this occurs should be elucidated and intervention strategies designed. Intervention could save much psychological distress, since associated linear growth failure can exacerbate adolescents' feelings of being different and unwell.