PKD1, the locus most commonly affected by mutations that produce autosomal dominant polycystic kidney disease (ADPKD), has previously been localized to chromosome 16p13.3. Since no cytogenetic abnormalities have been found in association with ADPKD, flanking genetic markers have been required to define an interval--the PKD1 region--that contains the PKD1 gene. In this report we demonstrate, through the construction of a long-range restriction map that links the flanking genetic markers GGG1 (D16S84) and 26.6PROX (D16S125), that the PKD1 gene lies within an extremely CpG-rich 750-kb segment of chromosome 16p13.3. Approximately 90% of this region has been cloned in three extensive cosmid/bacteriophage contigs. The cloned DNA is a valuable resource for identifying new closer flanking genetic markers and for isolating candidate genes from the region.