Uinar–mammary syndrome (UMS) is an autosomal dominant disorder characterized by posterior limb deficiencies or duplications, apocrine/mammary gland hypoplasla and/or dysfunction, abnormal dentition, delayed puberty and genital anomalies. We report the mapping of a gene causing UMS to chromosome 1 2q23–24.1. Linkage analysis generated a positive lod score of 6.21 at θ = 0.00 with the marker D12S79, and recombinants bracket the UMS gene to a 21 cM region. This region contains a locus for Halt–Oram syndrome (HOS) suggesting that the genes for UMS and HOS may be allelic or closely linked. The identification of the gene causing UMS will be an important step toward understanding the molecular mechanisms that control limb and apocrine gland development.