Cystic fibrosis (CF) is one of the most common autosomal recessive and multisystemic diseases. CF affects many systems. One of these systems is the endocrine and exocrine functions of the pancreas, causing cystic fibrosis-related diabetes, which is extremely complex and has unique pathogenesis. Maturity-onset diabetes of the young (MODY) is a rare type of diabetes with autosomal dominant inheritance and is not expected in patients with CF. In this study, we present MODY due to a novel glucokinase gene mutation, which is an unexpected form of diabetes in patients with CF. This is previously unreported in the literature.