Unilateral multicystic dysplastic kidney (MCDK) in a normal infant is believed to be a sporadic disorder, with an incidence of about 1 in 4,300 live births. Isolated unilateral MCDK occurring in a family without other genitourinary abnormalities has not been described. We report a family in which isolated unilateral MCDK occurred in a woman and her two children. The mother presented with a palpable abdominal mass during infancy, which on excision was found to be a MCDK. Both the children were found to have MCDK on prenatal ultrasonography, which was later confirmed on postnatal evaluation. The MCDK in the children continues to involute on follow-up urinary tract ultrasonography. The inheritance of MCDK appears to be autosomal dominant in this family.