This study tested the hypothesis that adolescents with attention deficit hyperactivity disorder (ADHD) exhibit a higher prevalence of caries than adolescents in a control group. Thirty-two adolescents with ADHD and a control group of 55 adolescents from a population-based sample, all 17 yr of age, underwent a clinical and radiographic dental examination. The mean +/- SD number of decayed surfaces (DS) was 2.0 +/- 2.2 in adolescents with ADHD and 0.9 +/- 1.4 in adolescents of the control group. Thirty-one per cent of the adolescents in the ADHD group had no new caries lesions (DS = 0) compared with 62% in the control group. Six per cent of the adolescents in the ADHD group were caries free [decayed, missing or filled surfaces (DMFS) = 0] compared with 29% in the control group. Adolescents with ADHD also had a higher percentage of gingival sites that exhibited bleeding on probing compared with the control group: 35 +/- 39% vs. 16 +/- 24% (mean +/- SD), respectively. At 17 yr of age, adolescents with ADHD exhibited a statistically significantly higher prevalence of caries compared with an age-matched control group. Adolescents with ADHD need more support regarding oral hygiene and dietary habits. They should be followed up with shorter intervals between dental examinations to prevent caries progression during adulthood.