BACKGROUND: Multiple sclerosis (MS) is a neurological degenerative chronic condition without cure. However, long-term disease-modifying therapies (DMTs) help reduce the severity of MS symptoms. Adherence to DMTs is key to their success. Several studies have analyzed what makes patients adherent to their DMTs. As new DMTs have entered the market, few studies have analyzed factors of adherence using all currently available DMTs. OBJECTIVE: To analyze different factors of adherence to DMTs for MS, in particular how the type of DMT affects adherence. METHODS: This retrospective cohort study used enrollment and claims data from an upper Midwest health plan in the United States between 2011 and 2013. Patients entered the study if they had any medical claim with an MS diagnosis and used only 1 DMT during the study time frame. Medication possession ratios (MPRs) were computed as the fraction of days with medication supplied during the year; patients with MPRs of 0.8 or higher were considered adherent. Multivariate probit models with patient-specific random effects were estimated, with controls for demographic characteristics, type of DMT, health plan type, and measures of health status. RESULTS: Patients aged over 45 years were between 13.7 to 18.6 percentage points more likely to be adherent than younger patients. Women had a 5.5 percentage-point lower probability of being adherent than men. Patients using self-injectable DMTs with injection site reactions as the most likely side effect were 9.1 percentage points less likely to be adherent than patients using oral, infusible, and other self-injectable DMTs. Patients with depression had a 5.5 percentage-point lower probability of being adherent. These results were robust to changes in controls for type of plan and neighborhood socioeconomic characteristics. CONCLUSIONS: This study found statistically significant differences in adherence to DMTs by age, sex, type of DMT, and a depression diagnosis.