To further delineate the clinical and developmental features of Angelman syndrome, we collected data through three sources of information: (1) physical examinations; (2) laboratory data and family questionnaire data of affected individuals; and (3) literature review. The questionnaire data describes a generally normal prenatal and birth history. Feeding difficulties, developmental delay, or seizures were the presenting problems in all infants. The diagnosis of Angelman syndrome, however, was not made in any infant prior to 1 year of age. Except for seizures, no medical or surgical complication was common, although a variety of visual complaints or findings were common. Sixty percent of Angelman syndrome children had a cytogenetically demonstrated deletion of chromosome 15q11-q13. The individuals with and without a deletion could not be differentiated clinically. Diagnosis in early childhood is therefore difficult, and a high index of suspicion is recommended.