To evaluate the presence of diabetic cardiomyopathy, we measured various parameters of left ventricular systolic and diastolic function by means of M-mode and Doppler echocardiography in 50 IDDM children (mean age 13 +/- 3 years; mean IDDM duration 5.9 +/- 4.1 years) free of cardiovascular symptoms. As compared to age-matched healthy control subjects, diabetic children evidenced a significant increase in mean values of pressure half time (PHT), an index of the early diastolic phase (53.7 +/- 10.2 msec vs 44.5 +/- 9, p < 0.002). When the patients were subdivided on the basis of IDDM duration, metabolic control and the presence of retinal microangiopathic abnormalities, those with longer IDDM duration and poor glycemic balance had higher PHT values. These data indicate that an early diastolic dysfunction, expressed by reduced left ventricular compliance, can be found in children with Type 1 diabetes mellitus of relatively short duration. Doppler echocardiography is a reliable non-invasive means to assess early impairment of cardiac function in IDDM patients.