The insulin-like growth factor I (IGF I) receptor is a tyrosine kinase-containing transmembrane protein that plays an important role in cell growth control. We have isolated and characterized human genomic DNA clones containing the entire coding sequence of the IGF I receptor. Results of restriction analysis and sequencing of multiple overlapping clones were consistent with the existence of a single IGF I receptor gene. The complete receptor coding sequence is contained in 21 exons. There is striking homology with the insulin receptor gene in overall size (approximately 100 kilobases) and in the number and size of individual exons. An exon analogous to the alternatively spliced exon 11 of the insulin receptor gene could not be detected. An alternative internal splice site corresponding to a known alternatively spliced mRNA transcript was shown to be located at the 5' end of exon 14. Knowledge of the structure of the IGF I receptor gene should facilitate further studies on the structural determinants of receptor function, the relationships between insulin and IGF I receptors, and the molecular basis for multiple IGF I receptor species.