OBJECTIVE: To compare osteoporosis treatment charges among patients treated with an estrogen versus a selective estrogen receptor modulator (SERM) in a managed care population. METHODS: Patients ³40 years of age with a diagnosis of osteoporosis between January 1 and June 30, 1999 and ³2 pharmacy claims for an estrogen or SERM were selected from the PharMetrics Integrated Outcomes Database. Patients were excluded if they had less than 6 months of continuous enrollment following the first (index) prescription claim for an estrogen or SERM or received other drugs for osteoporosis, such as bisphosphonates or calcitonin-salmon. The frequency of of hip, vertebral, forearm/wrist or other fracture and/or related surgical procedures and osteoporosis-specific charges were assessed over the 6-month period following the index prescription. RESULTS: 252,892 patients met the selection criteria, including 245,650 treated with estrogen and 7,242 with SERMs. The estrogen cohort was significantly younger than the SERM cohort (mean age: 54.3 vs. 59.0 years, p<0.001) and had less frequent fractures/surgical procedures (1.0% vs. 1.6%, p<0.001). The SERM group had higher mean osteoporosis-related pharmacy ($309 vs. $106) and medical charges ($73 vs. $29) resulting in a total charge difference of $247 (p<0.001). Stratified analyses indicated that the SERM cohort had consistently higher mean charges across all age ranges compared to the estrogen cohort. CONCLUSION: In this initial cost comparison between SERM and estrogen therapy for osteoporosis, short-term (6-month) osteoporosis-related charges were significantly higher in the SERM group primarily due to the difference in drug costs. Longer-term studies are required to examine all of the costs associated with these therapies.