OBJECTIVES: To compare the leuprorelin UK licensed dose (3.75mg) with the USA licensed dose (7.5mg) in the treatment of prostate cancer. METHODS: Systematic review of CENTRAL, BIOSIS, EMBASE and MEDLINE for clinical trials in patients with prostate cancer treated with leuprorelin was conducted in March 2008. Data on overall response (a composite of complete response, partial response and stable disease) were extracted. Summary effect estimate (Relative Benefit, RB) was calculated by meta-analysis using Bayesian Markov Chain Monte Carlo simulation. The probability of a treatment having the greatest overall response was calculated as the proportion of simulations in which that treatment had the greatest relative efficacy. RESULTS: Of the 1242 papers initially identified in the literature search, only 4 were found to be head-to-head comparisons of leuprorelin 3.75mg vs 7.5mg. Two of the 4 papers were reports of the same study, providing 3 studies for inclusion in the meta-analysis. The relative benefit of leuprorelin 7.5mg over 3.75mg was found to be 11% (RB 1.11; 95% Credible Interval: 0.60 to 1.86), which equates to a mean absolute benefit of 9.1%. The probability of the higher dose being more effective than the lower dose was 68.1%. A sample size of 585 would be required for a clinical study designed to confirm the estimated 9.1% benefit of leuprorelin 7.5mg over 3.75mg (90% power, 5% significance level). A similar study of 5590 patients would be required to confirm the clinical equivalence of the two doses (assuming minimum clinically important overall response 3%), providing the study failed to demonstrate a 3% difference. CONCLUSIONS: A Bayesian meta-analysis of the available evidence suggests that leuprorelin 7.5mg may be more effective in terms of overall response than the 3.75mg dose. Further research is required to confirm the superiority of the higher dose or clinical equivalence between the two doses.