Background: Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, has been related with weight loss and energy balance. Some studies showed that leptin might be playing an important role in satiety, energy balance and immune response. The aim of this study was to evaluate serum leptin level in patients with PD and its association with clinical severity.Methods: In this cross-sectional study, 35 patients with PD and 51 healthy controls (HCs), matched for age, sex and body mass index (BMI), were recruited. Serum leptin level was measured and clinical characteristics and demographic data of patients were recorded.Results: The mean age of patients with PD and HCs were 59.80 ± 11.40 and 62.18 ± 11.60 years, respectively. Serum leptin concentration was not statistically different between patients with PD and HCs (21.1 ± 23.1 ng/ml vs 25.9 ± 21.8 ng/ml, P = 0.280). There was no relation between plasma level of leptin and clinical severity of patients with PD.Conclusion: Our findings suggest that serum level of leptin is neither implicated in the pathogenesis of PD, nor decreases as disease progresses.