Mannan-binding lectine (MBL) is a protein implicated in immune response in children. Children are more prone to develop pathologies like infection, autoimmune disease, cystic fibrosis, liver disease. The aim of the study was to evaluate the MBL serum levels in children with cystic fibrosis, liver disease, compared to controls. Subjects with cystic fibrosis and liver disease were aged matched with controls, blood samples were collected. MBL was determined by solid-phase enzime-linked immunoabsorbent assay. In the group of subjects with liver disease associated with cystic fibrosis, the average was 2061.99 ng/mL, almost 50% lower than average level in the controls group (3986.827 ng.ml), being significantly low among children with cystic fibrosis and liver disease. In our study MBL values ranged from 2.3 ng/ml to 5432 ng/mL. Determining of MBL levels in children is suggestive for certain diseases, like cystic fibrosis liver disease and could be used as a predictive factor for early diagnosis and subsequent therapy.