OBJECTIVES: The present study examines whether findings from systematic biopsies add any prognostic information in men with clinical Stage T1-T2 prostate cancer treated with external beam radiation therapy alone. METHODS: Seventy-two men with clinical T1-T2 prostate cancer had ultrasound-guided quadrant or sextant prostate biopsies prior to treatment with external beam radiotherapy alone between January 1, 1988 and December 31, 1993. The median follow-up is 23 months (range, 11 to 65). Biochemical failure after irradiation was defined as a prostate-specific antigen (PSA) greater than 1.5 ng/mL (Hybritech assay) and rising. RESULTS: The biochemical relapse-free survival was 90% at 36 months. The percentage of biopsies involved by cancer was not predictive of biochemical relapse-free survival on univariate analysis. Patients with less than 50% positive biopsies had similar biochemical relapse-free survival at 36 months compared to patients with 50% or more positive biopsies (93% versus 89%; P = 0.80). After stratifying according to pretreatment PSA level, the percentage of positive biopsies was not prognostic. A multivariate analysis demonstrated that pretreatment PSA level was the only variable that predicted relapse-free survival (P = 0.01). CONCLUSIONS: At present, the results of ultrasound-guided quadrant or sextant biopsies do not add further prognostic information, beyond that provided by the pretreatment PSA level, in patients with T1-T2 prostate cancer treated with radiation therapy alone. Further follow-up will be required to confirm these results.