Left-ventricular wall thickness, measured by echocardiography, was determined in 111 normotensive diabetics (63 men and 48 women; mean age 26 +/- 9 years; diabetes duration 13.5 +/- 6.2 years) and 91 comparable control subjects. The interventricular septum was significantly thicker in diabetics than in controls: systolic 13.3 +/- 2.3 mm, diastolic 9.2 +/- 2.2 mm vs. systolic 12.5 +/- 2.1 mm and diastolic 8.9 +/- 1.7 mm (P less than 0.05). Posterior wall thickness measurements were: systolic 15.8 +/- 2.2 mm vs 14.6 +/- 2.0 mm (P less than 0.001), diastolic 9.5 +/- 1.8 mm vs 8.4 +/- 1.3 mm (P less than 0.01). Left-ventricular wall thickness increased stepwise with increasing severity of microvascular complications (retinopathy, nephropathy, neuropathy). There was a moderately close correlation between blood pressure values and the degree of microvascular complications (r = 0.49, P less than 0.01). These correlations indicate that increases in wall thickness are diabetes specific, but may be influenced by the level of blood pressure.