Background: Chromosome 22q11 deletion (del22q11), the most common microdeletion syndrome, causes a wide spectrum of clinical disorders. Recent studies have suggested that significant psychiatric and behavioral disturbances occur in up to 60% of these individuals. Objective: To illustrate the spectrum of behavioral and psychiatric abnormalities associated with del22q11 and the subtle nature of its associated physical findings. Patients and Methods: Case series describing psychiatric and behavioral findings in 3 patients with del22q11. Results and Conclusions: Behavioral and psychiatric problems are common in patients with del22q11 syndrome. Because the physical manifestations of the disorder are so variable and may be subtle, the behavioral and psychiatric manifestations may be the presenting problem. Providers must therefore consider del22q11 as a potential diagnosis in children and adults with behavioral and psychiatric problems. Furthermore, behavioral and psychiatric problems need to be looked for when caring for children and adolescents with a known diagnosis of del22q11.