Individuals with Angelman syndrome (AS) have severe learning disability, ataxia, seizures, dysmorphic facies, a happy, sociable disposition, and inability to speak. Most of the literature concerning the clinical features of AS has concentrated on younger children. This study aimed to look at the natural history of AS by documenting the clinical features in a group of 28 adolescents and adults with AS (12 males, 16 females; age range 16 to 40 years). Specific aspects studied included physical characteristics, general health, mobility, seizure disorder, behaviour and communication, and self-help skills. Problems seen in this older group of individuals differed significantly from those typically observed in younger children. The incidence of scoliosis and joint contractures increased with age. Facial features were more striking in adults. Hyperactivity and concentration improved and the sociable disposition persisted. There were subtle clinical differences between the groups of individuals with different underlying genetic abnormalities. Information obtained from this study is relevant to diagnosis and management of older individuals with AS.