<h4>Background</h4>Males with multiple sclerosis (MS) have a higher risk for disability progression than females, but the reasons for this are unclear.<h4>Objective</h4>We hypothesized that potential differences in TSPO-expressing microglia between female and male MS patients could contribute to sex differences in clinical disease progression.<h4>Methods</h4>The study cohort consisted of 102 MS patients (mean (SD) age 45.3 (9.7) years, median (IQR) disease duration 12.1 (7.0-17.2) years, 72% females, 74% relapsing-remitting MS) and 76 age- and sex-matched healthy controls. The gene discussed is TSPO; the disease is relapsing-remitting multiple sclerosis.