PURPOSE: We evaluated a prostate cancer-specific module in an unselected patient population. MATERIALS AND METHODS: A population study design was used to confirm the psychometric properties and clinical relevance of a prostate cancer-specific module, supplementing the standardized EORTC QLQ-C30 in Sweden. The study sample comprised 1,138 patients (81% response rate) examined by a mailout/mailback procedure 1.5 to 3.5 years after diagnosis. The standardized multitrait analysis method estimated the internal consistency and convergent and discriminant validity of 3 multi-item scales on sexuality, urinary symptoms and bowel symptoms. Confirmation of prostate-specific scales by disease stage and treatment used principal components analysis. The clinical relevance was tested by correlation analysis including disease and treatment-related parameters. RESULTS: Convergent and discriminant validity of all 3 prostate-specific scales was confirmed. The internal consistency was satisfactory for the sexuality and urinary scales (alpha 0.92 and 0.76, respectively), while the bowel scale failed to reach the alpha level of 0.70 required for group comparisons. The former scales showed invariance over all principal components analyses of subgroups (disease stage and treatment). The latter scale comprised differing numbers of items in the subgroup analyses, suggesting the use of single items at present. Descriptive data of the core and module questionnaires by disease and treatment-related parameters confirmed their interpretability and thus their clinical usefulness. CONCLUSIONS: The presented self-report questionnaire technique has great potential to inform clinicians about the quality of life in patients suffering from prostate cancer.