Inactivation of the von Hippel-Lindau tumor suppressor gene is linked to the development of hereditary (VHL Disease-associated) and sporadic clear cell carcinoma of the kidney. The VHL gene product, pVHL, targets the heterodimeric transcription factor HIF for polyubiquitination, and restoration of pVHL function in VHL(-/-) renal carcinoma cells suppresses their ability to form tumors in nude mice. Here we show that tumor suppression by pVHL can be overridden by a HIF variant that escapes pVHL control. These studies prove that HIF is a critical downstream target of pVHL and establish that activation of HIF target genes can promote tumorigenesis in vivo.