Quality of life (QoL) is now commonly studied in prostate cancer. However, little is known about the appropriateness of the various QoL instruments in this group of patients. The purpose of this work was to study the baseline QoL assessment of patients with prostate cancer who were randomised into three EORTC phase III studies. The three trials included locoregional prostate cancer patients, poor prognosis metastatic patients and hormone resistance patients, respectively. In the three trials, patients were asked to complete a questionnaire assessing their physical and psychosocial functioning and their symptom levels. These questionnaires included questions from the EORTC QLQ-C30 (version 1): the physical functioning, role functioning, global health/QoL scales and a single pain item. The psychometric properties of the scales were assessed and an analysis was performed to investigate if differences existed in the scale scores between the three groups of patients, 638 baseline questionnaires were available for patients entered into the three trials. The Gutman coefficients of reproducibility and scalability were 0.94 and 0.71, respectively, for the physical functioning scale and 0.97 and 0.90, respectively, for the role functioning scale. The Cronbach's alpha reliability coefficients were 0.68, 0.48 and 0.90 for the physical functioning, role functioning and global health/QoL scales, respectively. The four scales were able to distinguish clearly between the patient populations under study. The physical functioning, role functioning, global health/QoL scales and the single pain item scale from the EORTC QLQ-C30 (version 1) are valid measures when used in the setting of prostate cancer.