<b><i>Background:</i></b> The mechanisms of fat mass (FM) loss in cystic fibrosis (CF) are poorly understood but could represent complex pathways involving dysregulation of appetite-modulating peptides and an amplified inflammatory response. Nesfatin-1 is a newly described peptide that decreases food intake and FM but has not been studied in CF. <b><i>Objectives:</i></b> We hypothesized that changes in the appetite-suppressing hormone nesfatin-1 would be physiological, and levels would be lower in advanced CF patients with lower FM compared to those with milder disease and healthy controls. We determined the levels of the cytokines TNF-α, IL-1β, and IL-6 as they have been associated with weight loss in disease states. <b><i>Methods:</i></b> Fifty-four adult CF subjects, i.e. 17 with severe, 22 with moderate, and 15 with mild disease, as well as 18 controls were recruited. PFT and body composition analysis (via bioelectrical impedance) were performed. Nesfatin-1 and cytokine levels were determined by ELISA. <b><i>Results:</i></b> Contrary to our proposed hypothesis, nesfatin-1 levels were highest in CF patients with severe disease and the lowest FM. A significant negative correlation between nesfatin-1 levels and FM was found only in the severe CF group (r = -0.7, p = 0.003). In forward stepwise regression analysis, only FM was significantly associated with nesfatin-1 levels. Levels of TNF-α and IL-6 were elevated in the severe CF group, but there was no association with either FM or nesfatin-1. <b><i>Conclusion:</i></b> In advanced CF and low FM, nesfatin-1 plasma levels are significantly increased and inversely correlated with the FM. Our results further suggest that nesfatin-1 exerts its effects independently of TNF-α or IL-6.