Type 1 diabetes (TD1) is characterized with elevated blood glucose due to insulin deficiency. In case of insulin deficiency glucose can not be used by the body cells to generate energy. Therefore, triglycerides (TG) and free fatty acids (FFA) become source of energy. Ketone bodies (KBs) are synthesized through beta oxydation of FFAs in the liver. KBs serves as an alternative source of energy. The ability of muscle cells to use KBs in energy production is dependent the insulin. Insulin deficiency in individuals with T1D causes both the increased synthesis of KBs and also inability to use the KBs as source of energy. Accumulation of KBs in the blood is known as hyperketonemia (ketosis). Elevated KBs cause a decrease in blood pH, thereby, a diabetic complication diabetic ketoacidosis develops. On the other hand ketosis in individuals with T1D can develop due to insulin deficiency and prolonged hyperglycemia, as well as prolonged fasting state or prolonged and intensive physical exercises. In this study, we present hyperketonemia situation in a child with T1D that was atributed to the intensive physical exercises in and reviewed the relevant literature data.