Hepatomegaly, with or without abnormal liver function tests, was a common feature of both pediatric and adult patients with diabetes mellitus. We are reporting a case of a 16-year-old diabetic boy in whom we found hepatomegaly, mildly elevated transaminases and elevated serum lipids never noticed before. Abdominal ultrasound confirmed hepatomegaly; liver biopsy pointed out a picture compatible with glycogenosis. The patient's abnormal liver function tests, elevated serum lipids and hepatomegaly decreased over a period of 4 weeks with tight metabolic control. This situation was due to overinsulinization because the patient assumed an excessive quantity of food and therefore took an excessive quantity of insulin. In conclusion, hepatomegaly may be seen in diabetic patients due to hepatic glycogen accumulation as a result of excessive food and insulin consumption. In hepatic glycogenosis, the pathological findings improve in 4 weeks when good metabolic control is provided. Therefore, the other reasons must be investigated when hepatomegaly persists for a longer period.