OBJECTIVE: To evaluate if mental fatigue is a symptom that appears independently from other clinical features in patients with Parkinson disease (PD), and to study if fatigue is persistent over time in these patients. METHODS: In 1993, 233 patients with PD were included in a community-based study of fatigue and followed prospectively over 8 years. Fatigue was measured by a combination of a seven-point scale and parts of the Nottingham Health Profile (NHP) at baseline and after 4 and 8 years. In addition, the Fatigue Severity Scale (FSS) was used to evaluate fatigue in 2001. Population-averaged logistic regression models for correlated data were performed to study the relationship between fatigue and various demographic and clinical variables. RESULTS: In patients who were followed throughout the 8-year study period, fatigue increased from 35.7% in 1993 to 42.9% in 1997 and 55.7% in 2001. Fatigue was related to disease progression, depression, and excessive daytime sleepiness (EDS). However, the prevalence of fatigue in patients without depression and EDS remained high and increased from 32.1% to 38.9% during the study period. For about 44% of the patients with fatigue the presence of this symptom varied during the study period, as it was persistent in 56% of the patients with fatigue. CONCLUSIONS: The authors confirmed the high prevalence of mental fatigue in patients with Parkinson disease (PD). Fatigue is related to other non-motor features such as depression and excessive daytime sleepiness, but cannot be explained by this comorbidity alone. In more than half of the patients mental fatigue is persistent and seems to be an independent symptom that develops parallel to the progressive neurodegenerative disorder of PD.