 The 800 early PD subjects in this study have already been evaluated clinically and have undergone longitudinal dopamine transporter DAT imaging with 123I ß-CIT baseline and 22 months. In Follow-up imaging will be performed at 24-month intervals 46 and 70 months following PRECEPT baseline. All scanning procedures will be performed at the Institute for Neurodegenerative Disorders IND using methods previously employed in the PRECEPT study. 