Objectives. To evaluate prospectively the health-related and disease-specific quality of life (QOL) at diagnosis and during the first year thereafter for patients with newly diagnosed prostate cancer who received care at Veterans Affairs Medical Centers. Methods. Interviewers administered the European Organization for Research and Treatment of Cancer-QOL Questionnaire, a valid and reliable measure of health status, to 140 patients with prostate cancer at baseline (at diagnosis, before the initiation of treatment) and at 3 and 12 months thereafter at five Veterans Affairs Medical Centers. The mean changes from baseline values were analyzed statistically for patients with localized disease stratified by treatment group and separately for patients with metastatic disease. Results. Among the 98 men with localized prostate cancer, significant disease-specific QOL changes noted at 3 and 12 months included worsening of urinary and sexual function among men treated with radical prostatectomy or radiotherapy and worsening of urinary function among those who opted for watchful waiting (each P <0.05). Among the 42 men with metastatic prostate cancer, significant decrements in role and social and sexual function were noted at 3 months, but had resolved on average by 12 months of follow-up. Conclusions. At 12 months, disease-specific QOL decrements persisted for patients with localized disease, but for patients with metastatic disease, disease-specific QOL appeared to return to near baseline (at diagnosis, before treatment initiation) function. Our study, among the first to assess the QOL at baseline before treatment, provides meaningful information on general treatment effects, which are directly relevant to clinicians when discussing treatment options with patients. © 2003, Elsevier Science Inc.