Health-related quality-of-life (HRQOL) after a radical prostatectomy (RP) or external beam radiation therapy (EBRT) has not been studied in conjunction with oncological outcomes in relation to disease risk stratification. Moreover, the long-term outcomes of these treatment approaches have not been studied. We retrospectively analyzed oncological outcomes between consecutive patients receiving RP (n=86) and EBRT (n=76) for localized prostate cancer. HRQOL and functional outcomes could be assessed in 62 RP (79%) and 54 EBRT (79%) patients over a 3-year follow-up period (median: 41 months) using the Medical Outcomes Study Short Form-36 (SF-36) and the University of California Los Angeles Prostate Cancer Index (UCLA PCI). The 5-year biochemical progression-free survival did not differ between the RP and EBRT groups for low-risk (74.6% vs. 75.0%, P=0.931) and intermediate-risk (61.3% vs. 71.1%, P=0.691) patients. For high-risk patients, progression-free survival was lower in the RP group (45.1%) than in the EBRT group (79.7%) (P=0.002). The general HRQOL was comparable between the two groups. Regarding functional outcomes, the RP group reported lower scores on urinary function and less urinary bother and sexual bother than the EBRT group (P<0.001, P<0.05 and P<0.001, respectively). With risk stratification, the low- and intermediate-risk patients in the RP group reported poorer urinary function than patients in the EBRT group (P<0.001 for each). The sexual function of the high-risk patients in the EBRT group was better than that of the same risk RP patients (P<0.001). Biochemical recurrence was not associated with the UCLA PCI score in either group. In conclusion, low- to intermediate-risk patients treated with an RP may report relatively decreased urinary function during long-term follow-up. The patient's HRQOL after treatment did not depend on biochemical recurrence.