Objective: This research investigated the cognitive abilities and the working memory in children and youngsters with three different types of attention-deficit/hyperactivity disorder (ADHD): (a) mainly with attention-deficit, (b) hyperactive and impulsive, and (c) combined. Method: A computerized test called Infant Cognitive Abilities Test, which measures five cognitive abilities based on the Cattell-Horn-Carroll model, was used. Thirty-two children from both sexes, aged 7 to 15 years, from the Hospital das Clinicas, suffering from ADHD and a control group with 30 children from a state elementary school (first through eighth grades) were submitted to the test. Results: The results showed that there were significant differences with regard to the reaction time of the working memory of the different types of ADHD. Conclusion: Children suffering from ADHD had high test scores for the visual memory items of the test, when compared with the results in the auditory memory items. (Contains 9 tables and 3 figures.)