Study Objectives: Sleep problems are a common phenomenon in most neurological and psychiatric diseases. In Parkinson disease (PD), for instance, sleep problems may be the most common and burdensome non-motor symptoms in addition to the well-described classical motor symptoms. Since sleep disturbances generally become apparent in the disease before motor symptoms emerge, they may represent early diagnostic tools and a means to investigate early mechanisms in PD onset. The sleep disturbance, REM sleep behavior disorder (RBD), precedes PD in one-third of patients. We therefore investigated sleep changes in marmoset monkeys treated with 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine hydrochloride (MPTP), the non-human primate model for idiopathic PD. Design: Mild parkinsonism was induced in 5 marmoset monkeys (3M/2F) over a 2-week period of subchronic MPTP treatment. Electroencephalograms (EEGs) and electromyograms (EMGs) were recorded weekly. Motor activity and hand-eye coordination were also measured weekly, and any signs of parkinsonism were noted each day. Sleep parameters, motor activity, and performance data before and after MPTP treatment were compared between MPTP-treated marmosets and 4 control marmosets (1M/3F). Results: MPTP increased the number of sleep epochs with high-amplitude EMG bouts during REM sleep relative to control animals (mean ± SEM percentage of REM 58.2 ± 9.3 vs. 29.6 ± 7.7; P < 0.05). Of all sleep parameters measured, RBD-like measures discriminated best between MPTP-treated and control animals. On the other hand, functional motor behavior, as measured by hand-eye coordination, was not affected by MPTP treatment (correct trials MPTP: 23.40 ± 3.56 vs. control: 36.13 ± 5.88 correct trials; P = 0.32). Conclusions: This REM sleep-specific change, in the absence of profound changes in wake motor behaviors, suggests that the MPTP marmoset model of PD could be used for further studies into the mechanisms and treatment of RBD and other sleep disorders in premotor symptom PD.