The Vin-1 gene was initially identified as a gene whose expression is altered by the integration of proviruses in the Vin-1 common site of integration in retrovirus-induced rodent T-cell leukemias. We have now isolated the Vin-1 cDNA. Sequencing of the Vin-1 cDNA and Vin-1 exons revealed that the proviruses are integrated at the 5' end of the Vin-1 gene in an inverse transcriptional orientation. The sequence of the Vin-1 gene is identical to that of the recently identified G1-phase cyclin D2 gene. The human homolog of the Vin-1/cyclin D2 gene (CCND2) was mapped to chromosome 12, band p13.3, by in situ hybridization, confirming previous mapping data. Our results strongly support a role of the cyclin D2 gene in oncogenesis and thereby implicate altered cell cycle regulation in transformation.