Results of 999 patients with carcinoma of the prostate treated with radical radiotherapy were evaluated to assess the impact of pre-treatment transurethral resection of the prostate. (TURP). A total of 427 patients had a needle biopsy and 541 patients had a TURP. In 31 patients the diagnostic procedure could not be ascertained. In patients with stage T1/T2 disease (411) no adverse effect on prognosis was observed following TURP compared with needle biopsy. In patients with stage T3/T4 disease (534) a significantly higher distant relapse rate and cause-specific mortality were observed after TURP but overall survival was similar after TURP and needle biopsy. A significant correlation was observed between the probability of TURP and poorly differentiated cancers. Multivariate analysis which evaluated the influence of age, T stage, histologic differentiation and TURP did not demonstrate diagnostic TURP to be a significant independent prognostic variate for patients with prostate cancer managed by radical radiotherapy.