BACKGROUND: Ghrelin and peptide-YY (PYY) are two gut peptides with apparent opposing actions. In normal conditions, ghrelin and PYY work together in synergy to regulate energy homeostasis. During critical illness, series of metabolic, endocrine, and inflammatory changes take place in response to a severe insult. Emerging studies recorded alterations in gut hormone levels in critically ill adults. This study aims to assess the effect of inflammation, nutrition, and feeding status on ghrelin and PYY levels in critically ill children. METHODS: In this prospective study, we collected blood samples from critically ill children on days 2 or 3 of pediatric intensive care unit (PICU) admission for the analysis of serum ghrelin, PYY, and inflammatory markers. Data related to the intake anthropometry, as well as other clinical data, were collected from patients' records. Multiple linear regression analysis was used to identify factors affecting serum levels of these hormones. RESULTS: Forty-two children admitted to the PICU were included in this study. Ghrelin level was influenced by admission nutrition status of the children and age. PYY was influenced by macronutrient intake and age. Inflammatory markers also showed an association with the measured levels of these hormones, with C-reactive protein being positively associated with ghrelin levels and tumor necrosis factor alpha showing a positive association with PYY levels. CONCLUSION: Although ghrelin and PYY have been linked to feeding status in healthy patients, during critical illness there might be other factors, such as inflammation and nutrition status, that might contribute to the changes observed in ghrelin/PYY profiles.