Our purpose of this study was to investigate whether clinical rapid eye movement sleep behavior disorder (RBD) is indicative of more widespread degenerative changes in Parkinson's disease (PD), using a longitudinal cohort. In 2005 and 2007, we prospectively collected clinical and treatment characteristics of 61 consecutive patients with PD. The presence of RBD was assessed by spouse interview. Sixty-four percent of patients had clinical RBD in 2005, versus 52% of patients in 2007. The yearly incidence rate of clinical RBD onset was 9%, while clinical RBD disappeared in 14% of patients per year. The motor disability scores (when treated) were worse in patients with than without clinical RBD in 2005, but not in 2007. There was no difference between groups for frequency of freezing, falls, and hallucinations, or for scores on the depression scale, sleepiness scale, mini-mental state examination and frontal assessment battery at the beginning versus the end of the study. Patients with clinical RBD were disabled earlier than patients without RBD, but there was no specific worsening in the RBD group with time, either for motor or non-motor symptoms. The fluctuation and disappearance of clinical RBD in some patients may be due to functional abnormalities rather than lesions.