This study was undertaken to evaluate the quality of life (QoL) of previously untreated patients with M1 prostate cancer before and during androgen-suppressive treatment. Assessment of QoL was included as an optimal component of EORTC protocol 30853, a phase III trial comparing LH-RH (luteinising hormone-releasing hormone) analogue combined with a non-steroidal anti-androgen versus orchiectomy in patients with M1 prostate cancer. At pretreatment and during the follow-up period, patients were asked to complete a questionnaire assessing their physical and psychosocial functioning, and their symptom levels. Physicians rated the patients' performance status, pain, urological symptoms and erectile function. Due to its optional nature, only a minority of the patients in the trial were recruited for the QoL investigation. 63 patients completed a pretreatment questionnaire, of whom 49 completed a second questionnaire at least once during the initial 15 month follow-up period. While statistically significant correlations were observed between patients' and physicians' ratings of physical functioning and pain, these were of only a moderate magnitude (r = 0.43 and 0.30, respectively). No significant association was observed between physicians' and patients' ratings of micturation problems or of erectile function. Before treatment, fatigue, pain and decreased social role and sexual functioning were the problems most frequently reported by patients. With an average of approximately 1 year follow-up, statistically significant improvements were observed in patients' self-reported urological symptoms and metastatic pain. No significant changes were noted for the other QoL domains assessed. The results of this study confirm earlier findings that physicians' ratings may not reflect accurately the functional health and symptom experience of their patients. Patient-based QoL questionnaires offer the most direct means of evaluating the subjective morbidity associated with prostate cancer and its treatment. To increase participation and compliance rates in future studies, it is recommended that QoL assessment be made mandatory in those clinical trials in which QoL is considered to be an important study endpoint.