<b><i>Background:</i></b> Hepatic glycogenosis (HG) is a complication of poorly controlled type 1 diabetes mellitus (T1DM), characterized by glycogen accumulation in hepatocytes. Mauriac syndrome (MS) is a glycogenic hepatopathy, initially described in 1930, characterized by growth failure, delayed puberty, cushingoid appearance, hepatomegaly with abnormal liver enzymes, and hypercholesterolemia. HG is a condition with good prognosis and fast resolution after adequate glycemic control (although it has potential for relapse), with no case of evolution to end-stage liver disease described. <b><i>Case:</i></b> We describe a 26-year-old female, with T1DM complicated by severe retinopathy. The patient maintained poor glycemic control since childhood, presenting glycated hemoglobin persistently higher than 10% and recurrent episodes of ketoacidosis. In adolescence, she developed hepatomegaly and fluctuating elevation of aminotransferases and triglycerides. A small, nonrepresentative hepatic biopsy suggested macrovacuolar steatosis and mild fibrosis. After 15 years of diabetes, the patient was referred for gastroenterology clinic due to chronic diarrhea and exuberant hepatomegaly. Laboratory showed persistent elevation of aminotransferases and triglycerides. Bilirubin, iron metabolism, and coagulation were normal; viral serologies and autoimmune study were negative. Upper endoscopy, ileocolonoscopy, and enteroscopy presented no lesions. Abdominal magnetic resonance imaging displayed massive hepatomegaly. Liver biopsy was repeated showing marked nuclear glycogenization, mild steatosis, and no fibrosis; electron microscopy revealed very large deposits of glycogen and pleomorphic mitochondria with an unusually dense matrix, described for the first time in this entity. The diagnosis of MS variant and diarrhea due to autonomic neuropathy were assumed. <b><i>Conclusion:</i></b> Currently, HG is a well-recognized disease that occurs at any age and can be present without the full spectrum of features initially described for MS. In the era of insulin therapy, this entity represents a rare complication, caused by low therapeutic compliance.