Type 1 diabetes mellitus in children has been associated with other autoimmune diseases, especially coeliac disease and autoimmune thyroiditis. This association may be the result of a common pathogenic background. We describe the case of a girl with type 1 diabetes mellitus who developed icterus due to autoimmune hepatitis, a disease rarely found in children. Thyroiditis-associated and diabetes-associated autoantibodies were also present. Human leucocyte antigen typing revealed DRB1*03 heterozygosity, which has been associated with the occurrence of both autoimmune hepatitis and type 1 diabetes. This finding implies that similar pathogenic pathways may be involved in different autoimmune diseases including type 1 diabetes and autoimmune hepatitis. The patient was successfully treated with prednisolone and azathioprine. Autoimmune hepatitis can be a serious co-occurring disease in patients with type 1 diabetes.