There is an increasing interest in the diagnosis of attention-deficit/hyperactivity disorder (ADHD) in adulthood. It is also thought that ADHD is more prevalent in the field of intellectual disability (ID) than in the general population, but there are not many experimental studies. Since ADHD diagnosis in adults is more difficult, specific rating scales correlated to the main diagnostic systems have been created but have not been applied to people with ID. This work presents an application of an ADHD screening rating scale, the Conners' Adult ADHD Rating Scales (CAARS) screening version to 46 adults with ID. The resulting prevalence of "ADHD-positive" was 19.6%. These data are in accord with results reported in the general adult literature. Our data suggest that ID and attention disorders can co-occur. Therefore, not only can ADHD be a valid psychiatric diagnosis for a child with ID but for an adult with ID as well. The CAARS can be considered a useful clinical instrument to survey ADHD in ID.