BACKGROUND: Parkinson's disease (PD) affects patients' lives with more than just physical impairment. Many of the non-motor aspects of PD, such as cognitive impairment, depression, and sleep disturbances, are common and are associated with a variety of poor outcomes. However, at present, the pathophysiology and clinical management of these symptoms are poorly understood. OBJECTIVE: The authors sought to determine the associations between various illness-associated cytokines, cortisol, and the non-motor symptoms of PD. METHOD: The authors examined a panel of cytokines (IL-1β, IL-6, IL-10, TNF-α) and cortisol in a cohort of 52 PD patients with depression. RESULTS: There were a number of significant correlations between the non-motor symptoms and TNF-α. Specifically, the authors found that TNF-α (but not IL-1β, IL-6, IL-10, or cortisol) was significantly correlated with measures of cognition, depression, and disability. In regression analyses accounting for all variables, TNF-α was consistently significant in explaining variance in cognition, depression, sleep, and disability. CONCLUSION: These data are consistent with a growing body of literature that implicates inflammatory cytokines in neural and behavioral processes and further suggests that TNF-α may be involved in the production and/or maintenance of non-motor symptoms in PD.