Renal cell carcinoma of the clear cell type (ccRCC) is associated with loss of functional von Hippel–Lindau (VHL) protein and high, homogeneous expression of the G250 MN protein, an isoenzyme of the carbonic anhydrase family. High expression of G250 MN is found in all ccRCCs, but not in most normal tissues, including normal human kidney. We specifically studied the mechanism of transcriptional regulation of the CAIX G250 gene in RCC. Previous studies identified Sp1 and hypoxia-inducible factor (HIF) as main regulatory transcription factors of G250 MN in various non-RCC backgrounds. However, G250 MN regulation in RCC has not been studied and may be differently regulated in view of the HIF accumulation under normoxic conditions due to VHL mutations. Transient transfection of different G250 MN promoter constructs revealed strong promoter activity in G250 MN-positive RCC cell lines, but no activity in G250 MN-negative cell lines. DNase-I footprint and band-shift analysis demonstrated that Sp1 and HIF-1α proteins in nuclear extracts of RCC cells bind to the CAIX promoter and mutations in the most proximal Sp1 binding element or HIF binding element completely abolished CAIX promoter activity, indicating their critical importance for the activation of G250 expression in RCC. A close correlation between HIF-1α expression and G250 MN expression was observed. In contrast, no relationship between HIF-2α expression and G250 MN was seen. The participation of cofactor CBP/p300 in the regulation of G250 transcription was shown. In conclusion, HIF-1α and Sp1, in combination with CBP/p300, are crucial elements for G250 MN expression in ccRCC, and CAIX G250 can be regarded as a unique HIF-1α target gene in ccRCC.