A 17-year old woman noted myalgia after taking a long distance walk at the age of 10. In adolescence, she had several episodes of myalgia and pigmenturia after athletic activity or infection. At age 17, myoglobinuria and abnormally increased serum creatine kinase were documented after one of these episodes. The neurological examination revealed mild proximal muscle weakness of upper extremities. Electromyography showed myogenic patterns, such as brief, small abundant potentials on them. Venous lactate was raised normally on the ischemic exercise test. During prolonged fasting, plasma ketone bodies increased normally but there were abnormal elevations of plasma creatine kinase and myoglobin. Morphometric analysis of electron microscopy in muscle showed few lipid deposits and that of light microscopy revealed no abnormality. CPT activity in muscle was only 15% of normal value by the isotope-exchange assay. These results were consistent with the diagnosis of CPT deficiency. Although several cases of CPT deficiency with recurrent myoglobinuria have been reported in Western countries, our patients is the first case of Japanese showing recurrent myoglobinuria. CPT deficiency should be considered as a differential diagnosis in cases of recurrent myoglobinuria.