OBJECTIVES: Osteoporosis is a major public health problem in Asia. The objectives of this study were to compare the cost-effectiveness of different pharmaceutical treatments for Hong Kong women with established osteoporosis. METHODS: We compared the cost-effectiveness of treatments using a decision analytic model based upon Markov process for a hypothetical cohort of women at risk of fractures due to osteoporosis. A cohort of 100,000 postmenopausal women were simulated and followed for 10 years of treatment. The model included a number of scenarios based upon available pharmaceutical treatment alternatives in costs, clinical effectiveness, and time of treatment onset. Sensitivity analyses were performed to test the robustness of results. RESULTS: Programme costs, economic benefits, and cost-effectiveness ratios varied significantly among different treatments. Calcium and Alendronate are more cost-effectives than Calcitonin. Treatment efficiency has significant impact on the overall cost-effectiveness of the programmes. Later time of treatment onset improved the cost-effectiveness across programmes. While discounting and cost assumptions had some impact on the absolute value of cost-effectiveness ratios, they did not change the relative ranks of cost-effectiveness of different treatments. CONCLUSION: Calcium and Alendronate are more cost-effective treatments. As the population ages and more people are subjective to risks of fracture due to osteoporosis, policy formulating should consider the cost-effectiveness of the treatment as well as the time of treatment onset.