Aim: To study if age and non-behavioural measures of biological maturity have any associations with attention deficit hyperactivity disorder (ADHD). Methods: Two hundred fifty-one children 7 to 9 years of age in a Swedish school were screened for ADHD-symptom. ADHD-symptoms were estimated by Conners Abbreviated Questionnaire by both parents and teachers. Motor function, body weight and body height were measured. Skeletal age was estimated through hand radiographs. Results: Height, weight and skeletal bone-age did correlate significantly with age (rs = 0.44-0.69, p < 0.001) but not with ADHD symptom scores. Motor dysfunction had a weak negative correlation with age (rs = -0.21, p < 0.05). Parent and teacher scores of ADHD-symptoms did not correlate with age. Conclusion: This study showed that the variables measuring general biological maturity had a strong association with age, whereas motor dysfunction and ADHD symptoms had no significant association with age. ADHD symptoms did not correlate with the variables measuring general biological maturity. These results do not support the hypothesis that a general biological immaturity is an important etiologic factor for ADHD symptomatology. © 2007 The Author(s).