A group of 889 patients who completed radical X-ray therapy for transitional cell carcinoma of the bladder during a 12 year period were analysed by a multivariate technique. The patient's age, tumour category, tumour size and haemoglobin level were shown to be independent prognostic covariates. A prognostic index was derived and four prognostic subgroups were identified. The prognostic index could divide patients within each T category into those with good, moderate, fair or poor prognosis. The 5 year actuarial survival rate for patients in the poor prognosis group was 5.8% compared to 69.8% for patients in the good prognosis group. Durable local tumour control after radical radiotherapy was also analysed by a multivariate technique. Tumour category, grade, haemoglobin and urea level were found to be significant covariates. A tumour control index was derived and two groups were identified corresponding to a high probability of lasting local control after radical radiotherapy (47.8% of patients) or a low probability of control (52.2%).