Objective: To compare clinical and economic outcomes in women using LNG-IUS one year before and one year after insertion. Methods: Adult women (18+) prescribed LNG-IUS during 2003-2004 were identified in the MarketScan claims database (2002-2005). Only women with two years of continuous eligibility around the devise insertion date (1-year before and 1-year after insertion) were included. Clinical outcomes included were menorrhagia or irregular bleeding, dysmenorrhea, and fibroids-related symptoms. Economic outcomes included the number of emergency room visits, number of office visits, and health care costs. Both economic and clinical outcomes were measured and compared between the one year pre-insertion and one year post-insertion. McNemar's test was used to test for significant changes in dichotomous variables and the paired t test was used for continuous variables. Results: Three thousand nine hundred seventy-nine women received LNG-IUS. Mean age was 33.6 years (S.D.=6.7 years). During one year after the LNG-IUS insertion, women experienced significantly less dysmenorrhea (1.5% vs. 2.0%, relative risk [RR]=0.74, p=0.014) and less fibroids-related symptoms (2.1% vs. 2.4%, RR=0.86, p=0.046). No significant differences were found in menorrhagia or irregular bleeding. Emergency room visits also were significantly reduced (RR = 0.90, p<0.001). Outpatient office visits dropped from 12.5 visits during the pre-insertion year to 10.4 visits during the post-insertion year (p<0.001). The total direct health care costs were $5565 during the year before LNG-IUS use vs. $3141 during the year after, resulting in a $2424 reduction (p<0.001). The majority of the cost savings were due to the cost reduction associated with inpatient hospitalizations. Conclusion: During the first year after LNG-IUS insertion, women experienced significant less dysmenorrhea and fibroids-related symptoms. The use of LNG-IUS was also associated with reduction in resource utilization and health care costs.