This study assessed the prevalence and type of associated neuropsychiatric problems in children and adults with 22q11 deletion syndrome. One-hundred consecutively referred individuals with 22q11 deletion syndrome were given in-depth neuropsychiatric assessments and questionnaires screens. Autism spectrum disorders (ASDs) and/or attention deficit/hyperactivity disorder (ADHD) were diagnosed in 44 cases. ASD was diagnosed in 23 cases of whom only 5 had autistic disorder. ADHD was diagnosed in 30 individuals. In nine of these cases with ASD or ADHD there was a combination of these diagnoses. Mental retardation (MR) with or without ASD/ADHD was diagnosed in 51 individuals. ASD, ADHD, and/or MR were present in 67 cases. Females had higher IQ than males. The results of this study showed that the vast majority of all individuals with 22q11 deletion syndrome have behavior and/or learning problems and more than 40% meet criteria for either ASD, ADHD or both. Neuropsychiatric and neuropsychological evaluations are indicated as parts of the routine clinical assessment of individuals with 22q11 deletion syndrome.