© 2018 Wiley Periodicals, Inc. Introduction: Rasagiline is a monoamine oxidase B (MAO-B) inhibitor with possible neuroprotective effects in patients with amyotrophic lateral sclerosis (ALS). Methods: We performed a randomized, double-blind, placebo-controlled trial of 80 ALS participants with enrichment of the placebo group with historical controls (n = 177) at 10 centers in the United States. Participants were randomized in a 3:1 ratio to 2 mg/day rasagiline or placebo. The primary outcome was average slope of decline on the ALS Functional Rating Scale—Revised (ALSFRS-R). Secondary measures included slow vital capacity, survival, mitochondrial and molecular biomarkers, and adverse-event reporting. Results: There was no difference in the average 12-month ALSFRS-R slope between rasagiline and the mixed placebo and historical control cohorts. Rasagiline did not show signs of drug-target engagement in urine and blood biomarkers. Rasagiline was well tolerated with no serious adverse events. Discussion: Rasagiline did not alter disease progression compared with controls over 12 months of treatment. Muscle Nerve 59:201–207, 2019.