We report on a 25-year-old woman who was diagnosed with Weaver syndrome after reevaluation because of the family's concern regarding recurrence risk for mental retardation in offspring of the woman's brother. The diagnosis was suggested on the basis of postnatal growth excess, camptodactyly, and developmental delay, but with a somewhat atypical facial appearance. When childhood photographs were reviewed, her facial characteristics were more consistent with those of Weaver syndrome in early childhood, but became less obvious with age. This is the second adult reported with Weaver syndrome and provides documentation of the adult phenotype. The diagnosis may be more difficult to make in adolescents and adults if one uses criteria developed for facial manifestations in young children.