Objectives: Longitudinal assessment of a Parkinson's disease (PD) cohort, to investigate the evolution or REM sleep behavior symptoms (RED) over time and to test the relation between RBD at onset and motor dysfunction progression. Methods: An early stage PD cohort (n = 61) was assessed at two time points, separated by a two years interval. Diagnostic criteria for RBD were: violent behavior during sleep and body movements or vocalization indicative of dream enacting and at least six affirmative answers in the REM sleep behavior disorder screening questionnaire. Motor function assessment was performed with the Unified Parkinson's Disease Scale part II and III (total and partial scores for tremor, bradykinesia, rigidity, gait/postural instability and dysarthria). Results: 25 Patients had RED at baseline, vs. 35 at follow-up. Three RBD changed to non-RBD at follow-up, while 10 non-RED patients developed RED at follow-up (annual incidence of 12.5\%). RED and non-RBD patients did not differ significantly at baseline or follow-up. The presence of RBD at baseline was significantly related to an increase in UPDRS total and bradykinesia scores over time. Discussion: RBD symptoms can vary over time and have a tendency to increase during the early stages of disease. The presence of RBD symptoms could be a risk factor for motor function deterioration and particularly for bradykinesia worsening. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.