Most previous cases of unilateral terminal transverse defects of the hand have not been familial. Several previously reported cases of apparent autosomal dominant inheritance of such defects have subsequently been reclassified as type B brachydactyly. We report a pair of adult twin women with unilateral terminal transverse defects affecting the left hand in one woman and the right hand in the other woman. The latter woman has one daughter with a unilateral terminal transverse defect affecting the left hand. The hand anomaly is characterized by absence of the terminal portions of digits 2 to 5 with a mildly hypoplastic thumb (adactylia). Tiny nail remnants are evident on the remaining digital stumps, and no soft tissue syndactyly is apparent. At 2 years of age, the daughter has hypoplastic first, fourth, and fifth metacarpals with no ossification of the second or third metacarpals or any of the phalanges. The affected mother has hypoplastic metacarpals for digits 2 to 4 and a vestigial fifth proximal phalanx on the affected hand, with no other phalanges evident by roentgenogram other than those of the thumb. The mother's twin sister has similar findings, except the ossified phalangeal remnant is on her second and third fingers rather than her fifth finger. Doppler flow arterial patterns appeared normal in each hand of affected family members. The other hand and both feet are clinically and radiologically normal in each case, and the family history is negative for any other individuals with limb anomalies. A review of the literature suggests that this family may very well be unique.