The coronary collateral circulation of 162 patients suffering from atherosclerosis and coronary insufficiency (coronary artery disease) was studied. It was found to be present in 44 patients, or 27.1%; homocoronary in 9%, intercoronary in 90.9%. As other Authors have previously reported, anastomotic circulation is more developed when the coronary occlusion exceeds 75%. Not one of the 44 cases with normal coronary arteries or occlusion inferior to 75% presented collateral circulation. In addition, it was found to be present more frequently in cases with three branch lesions. The time of insurgence of coronary insufficiency seems to condition the development of anastomotic circulation which appears more frequently when the symptoms have been present for more than 5 years (43.9%). Anastomotic circulation is also found more frequently (48.4%) in patients who have suffered myocardial infarction and who have angina. Collateral circulation was not found in any of the 46 patients with unstable isolated angina; this seems to show the importance, in its pathogenesis, of the functional factor (spasm). In conclusion, we may say that anastomotic circulation is more developed: 1) in cases of severe occlusive lesions (in severe coronary occlusive disease/atherosclerosis) (85%);2) in three branch lesions; 3) in cases of long standing symptomatology; 4) in stable angina and in angina t infarction.