Background: Maturity-onset diabetes of the young (MODY) is a group of inherited disorders of non- autoimmune diabetes mellitus which usually present in adolescence or young adulthood. Patients and Methods: This cross-sectional study included 20 patients diagnosed with diabetes mellitus following up at Diabetes, Endocrine and Metabolism pediatric unit (DEMPU) Children hospital, Cairo University. The range of patients' age was 3 -18 years with mean diabetes duration of 1 year and 5 months. Genetic analysis of exon 5 of HNF1A gene was done using DNA sequencing method after a written consent was taken from the patient's guardian. Results: The mean age of patients is 12.1 years with range of 3 -18 years, mean age at diagnosis 10.77 years with mean diabetes duration 1 year and 5 months and mean HBA1c is 9%. All participants have family history of diabetes in at least 3 generations most of them diagnosed before age of 35 years as well as negative auto antibody (Anti GAD and Anti islet), measurable c peptide with mean of 0.45 nmol/litre. All patients showed no mutation in Exon 5 of HNF1A. Conclusion: Clinical suspicion of MODY 3 requires studying the whole gene for 10 exons and if negative, genetic testing for GCK, HNF1B, and HNF4A is highly recommended due to similarities in phenotype.