This study aims to examine the influence of risperidone on various attentional functions, including intensity and selectivity aspects of attention plus inhibitory control in children with attention deficit/hyperactivity disorder (ADHD) with co-morbid Disruptive Behavior Disorders (DBD) and normal IQ. Children with ADHD and DBD, aged 8-15 years, were treated with risperidone (mean daily dose: 1.5 mg; n = 23) and examined with three attentional paradigms before and after a 4-week treatment period. Age- and IQ-matched normal controls (n = 23) were also tested without medication on the same two occasions. No influence of the medication could be detected for any neuropsychological variable, neither as a positive enhancement nor as adverse side effects. However, clinical symptoms of ADHD and DBD assessed on the IOWA Conners Scale significantly improved after the 4-week treatment period. Divergent behavioral and cognitive effects of risperidone on ADHD symptoms were observed, with a significant reduction in behavioral symptoms, whereas no positive treatment effects were found on laboratory tasks of impulsivity. Thus, the cognitive effects of risperidone seem to differ from the cognitive effects of stimulant treatments in children with ADHD + DBD. However, no negative impact of risperidone was observed on attentional functions either, i.e., there was no slowing of cognitive speed.