Cell proliferation of transitional cell bladder cancer (TCC) was determined by PCNA (proliferating cell nuclear antigen)/cyclin immunostaining in 178 TCCs and the results were related to established prognostic factors, progression and survival during a mean follow-up period of 10 years. The fraction of PCNA/cyclin positive nuclei was related to T-category (P = 0.008), papillary status, WHO grade, DNA ploidy, S phase fraction, M/V index (volume corrected mitotic index) and AgNORs (silver stained nucleolar organiser regions) (for all P less than 0.001). TCCs presenting with pelvic lymph node metastasis at diagnosis had a significantly higher growth fraction than the tumours confined to the bladder wall (P less than 0.001). The fraction of PCNA/cyclin positive nuclei predicted progression in T-, N- and M-categories (P less than 0.001). In Ta-T1 tumours high fraction of PCNA/cyclin positive nuclei predicted metastasis (P = 0.019). In survival analysis the fraction of PCNA/cyclin positive nuclei predicted survival in the entire cohort (P less than 0.001) and in Ta-T1 tumours (P = 0.0005). In a multivariate survival analysis the fraction of PCNA/cyclin positive nuclei showed independent predictive value in the entire cohort (P = 0.046), in papillary tumours (P = 0.006) and in Ta-T1 tumours (P = 0.015). The results show that the growth fraction as determined by PCNA/cyclin immunostaining is a significant prognostic variable in TCC.