People who suffer from ADHD in their childhood are more likely to be involved in criminal acts in late adolescence and adulthood. This study analyses the association between retrospective ADHD symptoms and associated problems (somatic and learning difficulties), and current symptoms in a sample of adults from imprisoned and clinical populations. Four hundred and fifty‐seven participants, aged between 17 and 69 years, were divided into four groups: ADHD prison group without clinical history of symptoms (n = 61), prison group (n = 162), ADHD clinical group (n = 176) and clinical group (n = 58). The ADHD‐IV scale and Wender Utah Rating Scale (WURS) were administered to the four groups and demonstrated high rates of persistence of ADHD symptoms into adulthood. ADHD groups reported significantly higher impairment both during childhood (symptoms, somatic and learning difficulties) and at present, with the ADHD clinical group being the most severely impaired. Finally, current symptoms of ADHD, along with childhood ADHD symptoms and learning difficulties, significantly predicted current impairments, but only in the clinical group. These findings represent some initial steps into the identification of predictors of ADHD symptomatology in adulthood in order to elucidate its etiopathogenesis and better identify high‐risk groups for targeted prevention.