Autosomal dominant polycystic kidney disease (ADPKD) usually becomes symptomatic between the third and fifth decades. We studied ten families segregating for ADPKD in which children were observed with typical manifestations of the disease at birth or in early childhood. In these families, linkage analysis was carried out with a cloned DNA sequence from the alpha-globin locus known to be closely linked to the disease gene in adult onset ADPKD. In the families studied here, close linkage (theta max = 0.09 at zmax = 2.32) was also observed between the marker and disease loci. These results provide no evidence for genetic heterogeneity of ADPKD in families with early and adult onset.