We prospectively examined the changes of body weight among 468 individuals with Parkinson's disease (PD) before and after the diagnosis. The average weight of PD patients was stable until shortly before the diagnosis (p for trend = 0.2) and then declined (p for trend < 0.0001). Interestingly, PD patients tended to increase their energy intakes as their weights decreased (p for trend < 0.002). In conclusion, weight loss in PD patients appears to be a continuous process that starts several years before the diagnosis and is not caused by reduced energy intake.