Analogues of luteinising hormone releasing hormone (LHRH) have recently been introduced as an alternative to surgical orchidectomy in prostate cancer, but there has been concern about the economic costs of long-term treatment. The paper presents a comparison of costs for LHRH analogues versus orchidectomy in patients with advanced prostate cancer. The cost for the surgical procedure was estimated using data on patients treated with orchidectomy in Stockholm County, Sweden, during 1981-86. Estimates of costs for treatment with a depot LHRH analogue was based on observed treatment times among patients with symptomatic prostate cancer in a British randomised clinical trial of medical castration versus surgical orchidectomy. The average cost for orchidectomy was estimated at 2,580 pounds i.e. 7-31% less than for treatment with a depot LHRH analogue (2,760 pounds-3,380 pounds) assuming a mean treatment time in the range 19-23 months. The most cost-effective policy for castration was found to be initial treatment with an LHRH analogue followed by deferred orchidectomy after about 2 years among long-term responders. This policy would obviate the need for surgery in about 85% of the patients and the average cost (1,900 pounds) would be about 26% lower compared to that of a policy of primary orchidectomy in all patients.