Coronary atherosclerotic lesions are more often located eccentrically (70%) than concentrically (30%). In this study, the configuration of eccentric coronary artery atherosclerotic lesions was assessed by means of computerized planimetry in 100 specimens of eccentric arterial lesions. Special attention was given to the relation between the disease-free wall and the severity of obstruction. The mean disease-free wall are length measured between 17 and 23% of the total vessel circumference in eccentric coronary artery lesions that obstructed 50 to 90% of the cross-sectional area. This ratio persisted irrespective of the location of the lesion within the vessel and was not significantly different with vessels of different sizes. The presence of disease-free arcs of coronary artery wall as observed in this pathologic study may relate to three factors in clinical coronary artery disease: The published observations of spasm in segments of arteries harboring structural obstructive lesions may be explained by the frequent presence of uninvolved arcs of coronary artery walls. Multiple views during coronary arteriography are necessary to accurately reflect the degree of obstruction. The results of percutaneous transluminal coronary angioplasty may be influenced by both the disease-free arc and the atheromatous obstruction.