Medial arterial calcification (MAC) is a frequent vascular finding in patients with type II diabetes mellitus. Morphologically distinct from focal calcifications of atherosclerosis its radiographically distinct tramline pattern is frequently encountered in the arteries of the lower extremities. MAC is inconsistently related to age, duration and therapy of diabetes. In contrast, a strong association with diabetic polyneuropathy and familial aggregation have been documented. Although initially considered benign MAC is now recognized as a strong predictor of cardiovascular morbidity and mortality in diabetic patients. Investigations into MAC pathogenes and into its role in vascular pathophysiology are underway.