Background: The extent of myocardial ischaemia and the magnitude of systolic function impairment following myocardial infarction (MI) depend to a large degree on the performance of coronary collateral circulation. Endothelial function is altered in several disorders, including diabetes. An impaired development of coronary collateral circulation may be a factor responsible for post-MI complications in patients with diabetes., Aim: To compare the degree of coronary collateral circulation development between patients with advanced ischaemic heart disease (IHD), with or without diabetes., Methods: The study group consisted of 70 consecutive patients with diabetes who underwent coronary angiography between September 1998 and December 1999 and had total occlusion of at least one of the main coronary vessels. The control group consisted of 70 age-, gender, and MI history-matched non-diabetic patients. Coronary collateral circulation was assessed using the collateral score (CS)., Results: Patients with diabetes had less developed coronary collateral circulation than the patients without diabetes which was reflected by a significantly lower CS value - 1.47+/-1.56 vs 2.03+/-1.81; p < 0.05. No significant relationship was found between CS and age, gender, body mass index, history of MI or the presence of IHD risk factors. There was a significant association between the number of vessels with lesions and CS: r=0.40, p=0.0006 in the control group and r=0.42, p=0.0003 in patients with diabetes. The CS values in patients with single-, two- or three-vessel disease were 1.27+/-1.34, 2.38+/-1.85 and 2.98+/-2.07 in the control group, and 0.70+/-0.90, 1.10+/-1.30 and 2.23+/-1.76 in patients with diabetes, respectively. A multivariate analysis revealed that the presence of diabetes (t=-3.04, p=0.003) and the number of affected vessels (t=5.23, p=0.0001) were independently related to the CS values., Conclusions: Patients with IHD and diabetes have less developed coronary collateral circulation than IHD patients without diabetes, regardless of the extent of coronary lesions. Patients with diabetes who undergo coronary angiography, have more advanced coronary atherosclerotic lesions than patients without diabetes.