Accelerated coronary and peripheral vascular atherosclerosis is one of the most common and chronic complications of diabetes mellitus. A relatively recently analysed aspect of coronary artery disease in this condition is its silent or asymptomatic nature. We studied silent/asymptomatic myocardial ischaemia in unselected consecutive middle aged asymptomatic diabetics and controls by 24-hour ambulatory electrocardiographic monitoring, treadmill test and coronary angiography. Also, a relationship was sought between silent myocardial ischaemia and autonomic dysfunction. Thirty asymptomatic diabetics between the ages 35-60 without any documented evidence of coronary artery disease and as many controls (matched for age, sex, smoking habits, blood pressure, serum cholesterol and body mass index) were studied. All the diabetics and controls were subjected to treadmill test and 24-hour ambulatory electrocardiographic monitoring. Coronary angiography was done in those who were positive in treadmill test or 24-hour ambulatory electrocardiographic monitoring. Also five simple bedside tests for autonomic dysfuncton i.e. heart rate response to valsalva, deep breathing and orthostatic variation and blood pressure response to orthostatic variation and sustained handgrip were done in all the subjects. Those with two or more abnormal tests were diagnosed as having autonomic dysfunction. ST segment depression indicating silent myocardial ischaemia was seen in 14 (46.7%) out of 30 diabetics and in 3 (10.0%) out of 30 controls on both Holter and treadmill test (p=0.002). Also, diabetics had higher heart rate and greater number of supraventricular and ventricular ectopics than controls. Coronary angiography done in patients with silent ischaemia revealed higher prevalence of multivessel involvement and diffuse disease in diabetics as compared to controls. Half the diabetics (50%) and none of the control had autonomic dysfunction. Autonomic dysfunction was present in 85.7 percent of diabetics with silent ischaemia compared to 18.7 percent diabetics without silent ischaemia (p=0.001).