Febrile seizures are frequently accompanied by stress-induced hyperglycemia. Herein, we report the case of a 1.5-yr-old girl with hyperglycemia during febrile seizures who was subsequently diagnosed with glucokinase (GCK) maturity-onset diabetes of the young (MODY), considering its distinction from stress hyperglycemia. Following the development of febrile seizures owing to adenovirus infection, the patient presented a casual blood glucose level was 185 mg/dL. She had a multigenerational family history of diabetes and a hemoglobin A1c (HbA1c) level of 6.4%. Owing to the persistent glucose intolerance until the age of 5 years, genetic testing was performed, which revealed a heterozygous mutation in GCK, and the patient was diagnosed with GCK-MODY. Precise diagnosis of GCK-MODY individuals is important to avoid administering unnecessary antidiabetic medications. Even during hyperglycemia under stress, multigenerational diabetes and mildly elevated HbA1c levels can suggest GCK-MODY.