Despite increased interest in the role of effortful control (EC) in developmental disorders, few studies have focused on EC in autism spectrum disorders (ASD) and no study so far has directly compared children with ASD and children with ADHD. A first aim of this study was to investigate whether typically developing (TD) boys, boys with ADHD and boys with ASD can be differentiated based on EC levels. A second aim was to evaluate the relationship between EC and symptoms of ADHD and ASD. We assessed EC in 27 TD boys, 27 boys with ADHD and 27 boys with ASD (age 10-15) using different EC questionnaires. Clinical groups scored lower than the TD group on all EC total scales, but could only be differentiated from each other by means of self-reported persistence, impulsivity and activation control. Our data suggest that although EC is useful in differentiating TD boys from clinical groups, it is less efficient in distinguishing ADHD from ASD. Also, results suggest that EC plays a role in the manifestation of symptoms of both ADHD and ASD and that high levels of EC enable children to function more adequate in daily situations. (Contains 2 tables.)