Left ventricular diastolic function was studied in 29 young diabetic patients (aged from 14 to 44 years) without any clinical sign of heart disease. The metabolic state, the presence and the degree of microvascular and neuropathic complications have been established. Age and sex matched 32 healthy subjects served as controls. The parameters of left ventricular diastolic function were determined by means of phonomechanocardiography. By this method in diabetic patients impaired diastolic function of the left ventricle was found. This alteration could be best characterized by the values of normalized relaxation index referring to the isovolumetric relaxation of the left ventricle. A close correlation was found between the microvascular and neuropathic complications and the left ventricular diastolic dysfunction, while no correlation could be demonstrated between the metabolic state and the diastolic cardiac disorder.