In an investigation of myocardial metabolic abnormalities in hypertrophic myocardium, the myocardial glucose metabolism was evaluated with F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) in 32 patients with hypertrophie cardiomyopathy, and the results were compared with those in 9 patients with hypertensive heart disease. F-18-FDG PET study was performed in the fasting and glucose-loading states. The myocardial regional %dose uptake was calculated quantitatively. The average regional %dose uptake in the fasting state in the patients with asymmetric septal hypertrophy and dilated-phase hypertrophie cardiomyopathy was significantly higher than that in the patients with hypertensive heart disease (0.75 ± 0.34%, 0.65 ± 0.25%, and 0.43 ± 0.22%/100 g myocardium, respectively). In contrast, the average %dose uptake in the glucose-loading state in the patients with asymmetric septal hypertrophy and dilated-phase hypertrophie cardiomyopathy was not significantly different from that in patients with hypertensive heart disease (1.17 + 0.49%, 0.80 ± 0.44% and 0.99 ± 0.45%, respectively). The patients with apical hypertrophy had also low %dose uptake in the fasting state (0.38 ± 0.21%) as in the hypertensive heart disease patients, so that the characteristics of asymmetric septal hypertrophy and dilatedphase hypertrophic cardiomyopathy are considered to be high FDG uptake throughout the myocardium in the fasting state. Patients with apical hypertrophy are considered to belong to other disease categories metabolically. F-18-FDG PET study is useful in the evaluation of the pathophysiologic diagnosis of patients with hypertrophie cardiomyopathy.