OBJECTIVES To evaluate the late effects more than 2 years after radiotherapy using a patient-reported questionnaire in patients with prostate cancer enrolled in a randomized dose-response study comparing 70 Gy (conventional) and 78 Gy (conformal) radiotherapy (RT). METHODS The first 112 patients in the study were sent questionnaires to evaluate late bladder, rectal, and sexual function. There were 101 evaluable responses, with 50 in the conventional (Conven-RT) arm and 51 in the conformal (3DCRT) arm. RESULTS The overall rate of persistent incontinence was 29%, with 36% reporting urgency-related and 8% stress-related incontinence at some time after radiation. Use of a urinary protective device was required in 2%. The majority noticed leakage less than once per day (52%). In comparing the Conven-RT group with the 3DCRT group, similar incontinence rates were seen. However, fewer of those who received 3DCRT reported daily leakage of urine (33% versus 63%, P = 0.044). The majority (78%) of patients experienced no or mild change in bowel function after RT. Urgency of bowel movements (BMs) was of concern for 27% of patients; however, 90% reported their BMs were controlled without accidents, and 1% were taking antidiarrheal medications once a week or daily. The Conven-RT group had more moderate or major changes in bowel function than the 3DCRT group (34% versus 10%), more frequent BMs (47% versus 27%), and more urgent BMs (37% versus 18%) (P < or = 0.040 for all three comparisons). Hematochezia was uncommon, occurring once a week in 7% and daily in 4% of patients. Before RT, 80% of patients were potent, with erections adequate for intercourse at least a few times over the prior year. After RT, potency was decreased to 51%, with erections adequate for intercourse at least a few times since the completion of RT. CONCLUSIONS The overall rates of significant complications were extremely low. Although 30% reported incontinence, relatively few patients (2%) required pads. This rate compares favorably with the 31% of patients requiring protection after radical prostatectomy reported previously. Despite the higher treatment doses in the 3DCRT arm, slightly fewer long-term bowel side effects were noted. These data indicate that 78 Gy may safely be delivered using the conformal RT boost treatment technique described.