We report on the clinical and cytogenetic findings in 7 cases of inverted duplication of region 8p11.2p23. The phenotype of inv dup (8p) compiled from this series and the literature (N = 29) consists of severe mental retardation (100%), minor facial alterations (97%), agenesis of the corpus callosum (80%), hypotonia (66%), orthopedic abnormalities (58%), scoliosis/kyphosis (40%), and congenital heart defect (26%). A telomeric deletion of region 8p23.3-pter was confirmed in 3 of our cases studied using fluorescent in situ hybridization with a telomeric probe for 8p. Thus, these karyotypes are inv dup del(8) (qter-->p23.1::p23.1-->p11.2:). Our findings suggest that most cases of inv dup(8p) probably have a telomeric deletion.