Although physical therapy (PT) is effective in improving motor function in children with developmental coordination disorder (DCD), insufficient data are available on the impact of this intervention in children with combined attention-deficit-hyperactivity disorder (ADHD) and DCD. This prospective study aimed to establish the prevalence of DCD among a cohort of patients with ADHD, characterize the motor impairment, identify additional comorbidities, and determine the role of PT intervention on these patients. DCD was detected in 55.2% of 96 consecutive children with ADHD (81 males, 15 females), mostly among patients with the inattentive type (64.3% compared with 11% of those with the hyperactive/impulsive type, p less than 0.05). Mean age was 8 years 4 months (SD 2y). Individuals with both ADHD and DCD more often had specific learning disabilities (p = 0.05) and expressive language deficits (p = 0.03) than children with ADHD only. Twenty-eight patients with ADHD and DCD randomly received either intensive group PT (group A, mean age 9y 3mo, SD 2y 3mo) or no intervention (group B, mean age 9y 3mo, SD 2y 2mo). PT significantly improved motor performance (assessed by the Movement Assessment Battery for Children; p = 0.001). In conclusion, DCD is common in children with ADHD, particularly of the inattentive type. Patients with both ADHD and DCD are more likely to exhibit specific learning disabilities and phonological (pronunciation) deficits. Intensive PT intervention has a marked impact on the motor performance of these children. (Contains 3 figures and 1 table.)