The complete genomic sequence of the gene responsible for the predominant form of polycystic kidney disease, PKD1, was determined to provide a framework for understanding the biology and evolution of the gene, and to aid in the development of molecular diagnostics. The DNA sequence of a 54 kb interval immediately upstream of the poly(A) addition signal sequence of the PKD1 transcript was determined, and then analyzed using computer methods. A leucine-rich repeat (LRR) motif was identified within the resulting predicted protein sequence of the PKD1 gene. By analogy with other LRR-containing proteins, this may explain some of the disease-related renal alterations such as mislocalization of membrane protein constituents and changes in the extracellular matrix organization. Finally, comparison of the genomic sequence and the published partial cDNA sequence showed several differences between the two sequences. The most significant difference detected predicts a novel carboxy-terminus for the PKD1 gene product.