Velo-cardio-facial syndrome (VCFS) is associated with deletions at chromosome 22q11, abnormalities in brain anatomy and function, and schizophrenia-like psychosis. Thus it is assumed that one or more genes within the deleted region are crucial to brain development. However, relatively little is known about how genetic variation at 22q11 affects brain structure and function. One gene on 22q11 is catechol-O-methyltransferase (COMT): an enzyme that degrades dopamine and contains a functional polymorphism (Val158Met) affecting enzyme activity. Here, we investigated the effect of COMT Val158Met polymorphism on brain anatomy and cognition in adults with VCFS.