The microvascular density detected by markers of endothelial cells (ECs), such as CD31 and CD34, is considered to be a biomarker for angiogenesis, and it is generally associated with the malignant potential of solid tumors. However, there is a conflicting relationship between the microvascular density and prognosis in clear-cell renal cell carcinoma (ccRCC) patients. It may be explained by the suggestion that the microvascular density cannot fully reflect the angiogenic activity in ccRCC, as the markers of ECs are expressed by both quiescent and activated ECs. To investigate the real angiogenic activity, we examined vasohibin-1 (VASH1), a recently identified regulator of angiogenesis, which was demonstrated to be specifically expressed by ECs of newly formed blood vessels. Expression of VASH1 and CD34 were immunohistochemically examined in 116 primary untreated ccRCCs, 10 metastatic untreated ccRCCs, and 9 metastatic ccRCCs treated with sunitinib. ECs in the tumor microvessels were sporadically immunostained for VASH1, although no VASH1 staining was observed in the non-neoplastic renal tissues. CD34 was ubiquitously expressed by all ECs in both ccRCC and non-neoplastic renal tissues. Multivariate Cox analysis indicated that an elevated VASH1 density, but not microvascular density, was a significant and independent predictor of overall survival (odds ratio, 7.71; P=0.003). The microvascular density was significantly decreased in the sunitinib-treated metastases compared with untreated tumors (P=0.001). On the other hand, the VASH1 density was significantly higher in the metastatic ccRCCs treated with sunitinib compared with non-treated ones (P=0.010), indicating that VASH1 may be associated with the resistance of ECs to sunitinib treatment. Thus, VASH1 expression may reflect the actual activity of angiogenesis, and VASH1 can serve as a new prognostic and predictive biomarker in patients with ccRCC.