To determine the significance of p27(Kip1) (p27) for tumour behaviour and prognosis of patients with transitional cell carcinoma (TCC) of the renal pelvis and ureter. Using immunohistochemical staining, the relationship was evaluated between p27 protein level (low < 50%, high > 50%) and the Ki-67 labelling index (low < 30%, high > 30%) and clinicopathological features of 37 consecutive Japanese patients with TCC of the renal pelvis and ureter. Low levels of p27 correlated with higher tumour stage (P < 0.05) and positive lymph node metastases (P < 0.05). There was no significant association between p27 staining and the grade and tumour proliferation as assessed by the Ki-67 index. A high Ki-67 index correlated with higher grade and stage (P < 0.05). Kaplan-Meier plots of survival rate in patients with low or high p27 staining showed that low levels correlated with a shorter disease-free and overall survival (P < 0.001 and P < 0.01, respectively). Similarly, patients with a high Ki-67 index had lower disease-free and overall survival than those with a low Ki-67 index (P < 0.01 and P < 0.05, respectively). The Cox proportional hazards model showed that a low level of p27 was an independent predictor of a shorter disease-free (P < 0.01) and overall survival (P < 0.05) on univariate analysis, but not of overall survival on multivariate analysis. A high Ki-67 index was an independent prognostic marker for shorter disease-free survival on univariate and multivariate analysis (P < 0.01) and for overall survival on multivariate analysis (P < 0.05). In those with a high Ki-67 index, increased p27 staining was associated with a better prognosis than decreased staining for disease-free and overall survival (log-rank test, P < 0. 01 and P < 0.05, respectively). The finding that a low level of p27 is associated with tumour invasion and unfavourable prognosis indicates that p27 may be a useful prognostic marker for survival in upper urinary tract cancer.