We demonstrated that the gene responsible for a congenital limb deformity (polysyndactyly) maps to chromosome 7q36 in a large family. Pre- and postaxial anomalies of the extremities are inherited in this family as an autosomal dominant trait. The disease locus is closely linked to D7S550 (maximum lod score = 6.85, theta = 0). This region is homologous to a segment of mouse chromosome 5, where the mutations hammer toe (HM) and hemimelic extra toes (HX) have been mapped. These data suggest that human chromosome 7q36 and the homologous region of mouse chromosome 5 contain genes involved in limb pattern formation.