Objective: To assess in a noninterventional setting the prevalence and severity of fatigue in patients with Parkinson disease (PD). Methods: This was a cross-sectional study conducted in Italian patients with PD. Objectives included the evaluation of the current prevalence and severity of fatigue in patients with PD measured using the 16-item Parkinson Fatigue Scale (PFS-16), distressing fatigue (defined as a PFS-16 mean score $3.3), and assessment of its clinical correlates. Results: A total of 402 patients were enrolled and 394 patients completed the PFS-16 questionnaire with a PFS-16 mean (6SD) score of 2.87 6 0.99. Of these, 136 patients (33.8%) reported distressing fatigue (PFS-16 mean score $3.3). Patients with distressing fatigue were older (p 5 0.044) and had a longer duration of PD (p , 0.0001) than those without distressing fatigue. The presence of distressing fatigue was associated with higher total Unified Parkinson's Disease Rating Scale (UPDRS) scores, poorer quality of life (39-item Parkinson's Disease Questionnaire [PDQ-39]), worse social and psychological behaviors, a higher severity of depressive symptoms, and a higher prevalence of sleep disorders (all p , 0.001). Logistic regression analyses revealed that higher total UPDRS scores, female sex, depression, sleep disorders, as well as higher UPDRS activities of daily living scores and PDQ-39 mobility scores increase the likelihood of distressing fatigue in patients with PD. Conclusions: Approximately one-third of patients with PD have distressing fatigue, which is significantly associated with depression and sleep disorders. The fact that the presence of fatigue worsens patient quality of life supports the need to better diagnose and treat this debilitating symptom. © 2014 American Academy of Neurology.