p21Waf1 is a downstream effector of p53 and belongs to the Cip1/Kip1 family of cyclin-dependent kinase inhibitors. Thus, it is a potential tumor suppressor gene and likely plays an important role in tumor development. Moreover, reduced expression of p21Waf1 has been reported to have prognostic value in several human malignancies. In this study, we evaluated the prognostic value of p21Waf1 in bladder cancer compared with other clinicopathological features and with p27Kip1 and p53 expression. A total of 96 superficial (pTa-1) human bladder carcinomas were immunohistochemically stained for p21Waf1 protein expression. Positive p21Waf1 staining (> or =5% positive nuclei) was observed in 68 of the 96 (71%) tumors. p21Waf1 expression was neither associated with tumor stage (P = 0.9) nor with tumor grade (P = 0.18) but was significantly associated with both p53 protein expression (> or =20% positive nuclei; P = 0.007) and with p53 gene mutations (P = 0.017). A significant correlation was also observed between positivity for p21Waf1 and high (>50% positive cells) p27Kip1 expression (P = 0.04). With regard to prognosis, patients whose tumors showed absence of p21Waf1 staining displayed a significantly shorter overall survival (P = 0.01 by log-rank test). However, p21Waf1 expression did not correlate with disease-free survival (P = 0.15 by log-rank test). On a multivariate analysis that also included p53 and p27Kip1 expression, negative p21Waf1 staining was an independent predictor of reduced overall survival (P = 0.004; relative risk, 5.32), stronger than age and tumor stage. These data indicate that expression of p21Waf1 protein strongly correlates with survival and might represent a useful prognostic marker in primary superficial bladder carcinomas.