Cystic fibrosis is a rare genetic disease, and cystic fibrosis-dependent diabetes mellitus (CFDM) is its most common extrapulmonary complication, primarily associated with insulin deficiency. To date, few studies have been published on the treatment and management of adult patients with this disease. The oral glucose tolerance test is the most informative for screening CFDM but there are also publications on the possibilities of determining the content of glycosylated hemoglobin (HbA1c) to detect diabetes in patients with cystic fibrosis. There is limited evidence from randomized clinical trials to determine the optimal pharmacological treatment options for CFDM. Insulin is the most appropriate drug for the treatment of CFDM in current guidelines. This paper provides a review of publications on the diagnosis, screening and treatment of patients with cystic fibrosis and impaired glucose tolerance. The results of clinical trials studying the role of insulin therapy in CFDM are presented. Based on the analyzed data, it can be assumed that in CFDM, insulin is the drug of choice, improving glycemic control, nutritional status, and lung function. Therapy based on the use of transmembrane regulators of cystic fibrosis (CFTR-modulators) is considered promising.