DNA flow cytometric (FCM) data, histological features and clinical stage of bladder tumours in 222 patients were related to outcome during a mean follow-up of 10 years. Aneuploidy was detected in 82 (37%) of tumours and 140 (63%) were diploid. Intratumour heterogenity of DNA ploidy was found in 27% of 30 cases. Aneuploidy and high S-phase fraction (SPF) were related to clinical stage, histological grade and papillarity (P less than 0.0001). Aneuploidy (P less than 0.0001) and high SPF (P less than 0.0001) predicted metastasis to pelvic lymph-nodes and to distant sites. T category (P less than 0.0001), SPF (P less than 0.0001), histological grade (P less than 0.0001), papillarity (P = 0.0021), DNA aneuploidy (P = 0.0094) and G2 fraction (P = 0.0340) predicted cancer-related survival. Multivariate analysis showed DNA aneuploidy as the most important predictor of progression in T category (P = 0.0003) and T category was the most important predictor of lymph-node involvement (P = 0.0083) and metastasis (P = 0.0015), followed by FCM parameters. In Ta-T1 tumours SPF predicted progression independently (P = 0.0153). FCM offers more accurate prognostic information in Ta-T1 tumours than conventional methods. In invasive tumours, FCM offers quantitative prognostic information in terms of pelvic lymph-node metastasis and metastasis to distant sites.