Homozygotes of the mouse mutant limb-deformity (ld) reveal a reduced fertility and a high mortality of newborns. Unilateral and bilateral aplasia of kidneys is very common. In unilateral aplasia the right side is affected most, with no sex preference. All extremities show aplasias and synostoses, with 22 malformation types in the forelimbs and 8 types in the hindlimbs. Primary and secondary fusions of limb elements are found.