PURPOSE To use data from a prospective quality-of-life study to assess differences in disease-specific and general health-related quality-of-life changes after treatment with different external-beam irradiation techniques for prostate cancer. PATIENTS AND METHODS Patients were divided into three groups based on their pretreatment field size and planning technique: whole pelvis, small field, or conformal. Measures of bowel, urinary, and sexual function and of global health-related quality-of-life parameters (from the Health Survey Short Form [SF-36] and the Profile of Mood States [POMS]) were obtained from self-report questionnaires completed before initiation of therapy and at 3 and 12 months after therapy. RESULTS Irritative gastrointestinal and genitourinary side effects were frequent 3 months after treatment, but were substantially improved at 12 months. Sexual dysfunction increased steadily over the study period. The POMS and the SF-36 did not demonstrate significant changes over time. Despite small patient numbers, we found trends in favor of conformal therapy across several symptom measures, including sexual function. In the fatigue, energy, and vigor subscales, patients who received whole-pelvis treatment fared significantly worse than those in the other two groups. CONCLUSION Prospective, detailed data from a feasibility study allowed us to assess the effect of technique on quality of life following external-beam irradiation. Although limited by the small planned sample size, these results suggest that smaller radiation fields limit treatment-related complications, including, unexpectedly, sexual dysfunction. However, confirmation in a larger study is necessary.