Hyperthyrosis is a rare disease in early childhood typically characterized by tachycardia, restlessness, elevated body temperature, failure to thrive, diarrhoea, goiter and a tendency to hyperglycaemia. A 3-year old boy presented with typical symptoms of thyrotoxicosis accompanied by ketotic hypoglycemia and excessively high glutaric acid excretion. To our knowledge this association has so far not been described. Specific defects responsible for glutaric aciduria types I & II were excluded. Our patient suffered from glutaric aciduria type III which was described once and is characterized by mild metabolic signs.