PURPOSE To analyze the results of ultrasound-guided brachytherapy for stage T1-T2 prostate cancer, as shown by biopsy results. PATIENTS AND METHODS The 268 patients (mean age 66 years; range 41-83 years) underwent real-time ultrasound-guided implantation of either iodine-125 (N = 186) or palladium-103 (N = 82) seeds. Of these patients, 96 (36%) received total androgen suppression for 3 months prior to and 3 months after implantation. Prostate biopsy was performed 24 months later, with the six to eight cores all being interpreted by the same pathologist. Each specimen was rated either positive or negative for cancer. RESULTS Of the 268 patients, 238 (89%) had a negative biopsy at 24 months. Among the patients receiving androgen suppression, 2% were found to have positive biopsies compared with 16% of those not given hormones (P = 0.004). Of the 155 patients with stage T1-T(2a) cancer, 6% had a positive biopsy compared with 19% of patients with stage T(2b) or T(2c) cancer (P = 0.001). In the entire series, the pretreatment serum concentration of prostate specific antigen, Gleason score, and isotope (I v Pd) were not significant predictors of a positive biopsy. However, among the 172 patients who did not receive androgen suppression, all three factors were predictive: 42% for Gleason score of 7 to 10 v 13% for Gleason score < or =6 (P = 0.001): 25% for pretreatment PSA concentration >10 ng/mL v 13% for PSA < or = 10 ng/mL (P = 0.05); and 27% for stage T(2b) or T(2c) v 9% for stage T1 or T(2a) (P = 0.001). The isotope used and the last PSA value were not significant predictors. CONCLUSION Brachytherapy provides excellent local control of prostate cancer, with 89% of patients having negative biopsies 2 years after treatment. High-risk patients may benefit from the addition of androgen suppression.