OBJECTIVES: Due to the trade-offs between cost-sharing, patient-perceived value and health outcomes, the relationship between cost-sharing and DMTs utilization could be much more complex than monotonous. This study aimed to examine the relationship between out-of-pocket (OOP) payments for DMTs and DMT utilization.  It also explored for the existence of local optimum(s) in OOP payments with respect to the trade-off between health care utilization and cost containment. METHODS: Individuals with more than two MS diagnoses (ICD-9-CM: 340) and continuous plan enrollment were identified from the Thomson Medstat MarketScan Database (2006-2010). To avoid issues of patient selection of drugs, the OOP payment was measured based on the average OOP payment for purchasing a fixed basket of drugs at insurance plan level. We applied logistic regression on DMT utilization using OOP payment as main explanatory variable and demand elasticity was calculated based on the coefficient. We also used local linear regression to further explore the relationship between OOP payment and DMT utilization.  RESULTS: