BACKGROUND Maturity onset diabetes of the young type 2 (MODY) is an inherited disorder due to mutations in glucokinase (GCK) gene, which lead to mild fasting hyperglycemia. CASE PRESENTATION Herein an otherwise healthy 9-year old boy with hyperglycemia is presented in whom the diagnosis of MODY2 was suspected. Genetic studies showed heterozygous inactivating GCK gene mutation in exon 8 (c.1010delA) in this patient. The same mutation was found in his father as well. The patient received some dietary advices without any medication. CONCLUSION The identification of GCK mutation and diagnosis of MODY2 helps the clinicians to predict the disease course, prognosis and to exclude other types of diabetes.