With increasing media interest in prostate cancer and the availability of data to patients from support groups and the Internet, the knowledge and use of alternative therapies by patients is becoming more common. The purpose of our study was to quantify patient awareness and use of alternative therapies for the prevention and treatment of prostate cancer in the UK. In May 2000, we performed a survey of men attending our urology outpatient clinic for prostate cancer evaluation or follow-up. All men diagnosed with and those at high risk (abnormal prostate specific antigen) for prostate cancer were eligible for the study. Each eligible patient was then sent an anonymous 25-item questionnaire to explore their knowledge and use of various alternative therapies for prostate cancer. Out of 195 patients who were sent the questionnaire, 168 responded, for a response rate of 86%. One hundred and sixty-four were analysed. Eight-two out of 164 (50%) were aware of alternative therapies for prevention/treatment of prostate cancer, the most common were tomatoes/tomato-based products and low-fat diet. There were 27 (16.5%) respondents taking alternative therapies for their prostate. Private patients were more aware (60.4% private vs 46.2% NHS) of complimentary therapies and were more likely to take them (27.9% private vs 12.4% NHS) than National Health Service patients. The majority of patients (60%) had not informed their GP or urologist. Fifteen therapies and 12 medication sources were recorded. Asked if doctors should discuss non-prescribed therapies, even if there is no proven benefit, 62% said 'yes' while 29% said 'no'. Alternative therapy use for prostate cancer is likely to increase. If we don't ask patients specifically whether they are taking them, patients are unlikely to tell us. Urologists and clinical oncologists treating men with prostate cancer need to be aware of alternative therapies and have some understanding of any benefit or harm, not only to be able to answer patient's questions and offer advice, but also to consider interactions with other treatments.Prostate Cancer and Prostatic Diseases (2001) 4, 235-241.