Between 1951 and 1959, 148 cases of histologically confirmed carcinoma of the bladder have been treated with radium at the Rotterdam Radiotherapy Institute. Radium needles were implanted during suprapubic cystotomy. A spatial model of each implant was constructed in order to check the position of the needles and to facilitate the calculation of their optimal application time. An investigation has been made into the influence of various tumour and host factors on prognosis. In this series outcome is determined by local recurrence and by potential curability only. The factors analysed were histology, stage, size, site, multiplicity and diathermy of the primary growth, and the age, sex and concomitant disease of the patient. Stage appeared to be significantly (at P=0·05 level) related to five-year survival rate and hence to local recurrence rate and potential curability. This correlation was not dependent upon the size and grade of the tumour nor on the patient's age. Fulguration of the growth (two to six weeks prior to radium treatment or immediately preceding the insertion of the radium needles) coincided with a significantly better prognosis. This correlation was not due to other factors such as stage. Fulguration also affected local recurrence rate and potential curability, though not to a significant degree. The other factors analysed had no appreciable bearing on prognosis and were not linked to local recurrence rate nor generally to potential curability. The latter appeared to be influenced by grade; potential curability was significantly higher among patients with highly differentiated growths than among those with tumours of poor differentiation. Complications in this series consisted of early necrosis, late necrosis and calculus formation. Early necrosis, which was related to tumour size, to previous fulguration and to the sex of the patient, did not affect prognosis. Treatment results, considered by stage, are comparable to those reported from other radium centres. Between 1951 and 1959, 148 cases of histologically confirmed carcinoma of the bladder have been treated with radium at the Rotterdam Radiotherapy Institute. Radium needles were implanted during suprapubic cystotomy. A spatial model of each implant was constructed in order to check the position of the needles and to facilitate the calculation of their optimal application time. An investigation has been made into the influence of various tumour and host factors on prognosis. In this series outcome is determined by local recurrence and by potential curability only. The factors analysed were histology, stage, size, site, multiplicity and diathermy of the primary growth, and the age, sex and concomitant disease of the patient. Stage appeared to be significantly (at P=0·05 level) related to five-year survival rate and hence to local recurrence rate and potential curability. This correlation was not dependent upon the size and grade of the tumour nor on the patient's age. Fulguration of the growth (two to six weeks prior to radium treatment or immediately preceding the insertion of the radium needles) coincided with a significantly better prognosis. This correlation was not due to other factors such as stage. Fulguration also affected local recurrence rate and potential curability, though not to a significant degree. The other factors analysed had no appreciable bearing on prognosis and were not linked to local recurrence rate nor generally to potential curability. The latter appeared to be influenced by grade; potential curability was significantly higher among patients with highly differentiated growths than among those with tumours of poor differentiation. Complications in this series consisted of early necrosis, late necrosis and calculus formation. Early necrosis, which was related to tumour size, to previous fulguration and to the sex of the patient, did not affect prognosis. Treatment results, considered by stage, are comparable to those reported from other radium centres.