Rapid eye movement sleep behavior disorder (RBD) is a parasomnia characterized by brief recurrent episodes of loss of muscle atonia during rapid eye movement sleep, with enacted dreams that cause sleep disruption. Patients with multiple sclerosis (MS) have an increased risk compared with the general population to be affected by a sleep disturbance, including RBD. Patients affected, however, uncommonly can present RBD as the first clinical manifestation of MS without other neurologic deficits. These clinical presentations have usually been attributed to inflammatory lesions in the pedunculopontine nuclei, located in the dorsal pons. We present a case of RBD in a 38-year-old woman who was later diagnosed as having MS due to imaging findings and development of focal neurologic deficits. MS should be considered among the differential diagnoses in patients who present with symptoms of RBD, particularly if they are young and female.