The majority of follow-up studies show stability of deficits after treatment in adults with obsessive-compulsive disorder (OCD), regardless of improvement in symptomatology, and this suggests a possibly chronic dysfunction of the dorsolateral-striatal circuit. To our knowledge, this is the first study to explore the evolution of cognitive dysfunction in children and adolescents with OCD after treatment. A neuropsychological battery designed for this study was administered to 29 OCD patients aged between 7 and 18 years before and after 6 months of naturalistic treatment, and to 22 healthy subjects of similar age, sex and intellectual level. In the first assessment, the OCD group performed worse on some tests of memory, speed of information processing and executive functions, this being similar to the cognitive dysfunction described in adult patients. After treatment the cognitive profile of the OCD group was normalized, and many of the significant differences present in the first assessment disappeared. Children and adolescents did not show the stability in cognitive dysfunction described in studies with adults. Six months of effective treatment normalized cognitive performance in young patients, who showed an important response to treatment.