We report on clinical and cytogenetic data on 5 children and 2 adults with a de novo inverted duplication of the short arm of chromosome 8, and we give a review of 26 patients from the literature. The clinical picture in young children is characterized by minor facial anomalies, hypotonia, and severe developmental delay. In older patients the facial traits are less characteristic, spastic paraplegia develops, and severe orthopedic problems are frequent. Psychomotor retardation is always severe-to-profound. Duplication of 8p21-p22 results in a clinically recognizable multiple congenital anomalies/mental retardation (MCA/MR) syndrome. It is shown that in all patients examined, the duplication was accompanied by a deletion of the most terminal part of 8p.