Objectives: To determine the prevalence of obsessive--compulsive behaviours (OCB) in a clinical sample of children with attention-deficit hyperactivity disorder (ADHD) and to compare ADHD children (with and without OCB) with respect to clinical and cognitive characteristics and risk factors.
Method: We compared ADHD children (n = 134) with and without OCB, and we compared all ADHD children with a group of normal control subjects (n = 26) on various clinical, cognitive, and inhibitory control measures; neurobiological and psychosocial risk factors; and family histories of psychiatric illness.
Results: Clinically significant OCB was identified in 11.2% (15/134) of children with ADHD. Comorbid OCB was associated with significantly increased perfectionism, improved teacher ratings of inattention, and a decreased likelihood of having a first-degree relative with ADHD. Comorbid ADHD and OCB may also be associated with increased oppositional behaviour at home and better inhibitory control, though these differences were not statistically significant.
Conclusions: Comorbid OCB is common in clinically referred children with ADHD and is associated with increased impairment relative to ADHD alone. Further, children with ADHD and OCB may develop symptoms as the result of different genetic and environmental risk factors, compared with children with ADHD only.