Diabetes mellitus (DM) is a chronic, metabolic disease characterized by hyperglycemia developed due to lack of insulin and/or insulin effectiveness. The number of diabetic cases is rising and it is expected to double by 2035 to reach 600 million. The increase in means of molecular diagnosis has enabled detection of monogenically inherited diabetes types, except type 1 and type 2 diabetes with polygenic heredity. Monogenic diabetes phenomenon include, "Maturity Onset Diabetes of Youth" (MODY), mitochondrial diabetes, Wolfram syndrome, neonatal diabetes and special syndromes seen due to gene defects causing insulin resistance. This constitutes 2-5% of all diabetes cases. In monogenic diabetes, in which patients frequently receive a type 1 or type 2 DM misdiagnosis, the fact that the treatment varies according to etiology, increases the clinical importance of the rare disease. In this compilation, after pancreas embryology, insulin synthesis and secretion steps are briefly discussed, clinical and molecular pathologic features of monogenic diabetes will also be discussed.