REM sleep Behaviour Disorder (RBD) is a sleep disorder that can precedes the development of motor signs of Parkinson's disease by years. The aim of this study was to assess the functional integrity of nigrostriatal dopaminergic system in RBD patients using 123I-2b-carbomethoxy-3b-(4-iodophenyl)-N-(3-fluoropropyl) nortropane (123I-FP-CIT) Single-Photon Emission Computed Tomography (SPECT). 5 patients with RBD and 5 normal healthy controls were included in the study and underwent SPECT imaging 3 hours after injection of 111-185 MBq of 123I-FP-CIT. All RBD patients showed reduced 123I-FP-CIT striatal binding. 123I-FP-CIT SPECT is a useful diagnostic tool in RBD patients.