The registry contains information collected during 2003 from thirteen Spanish hospitals on the incidence, clinical presentation, initial course, diagnostic imaging, and treatment of anomalous coronary arteries originating in the contralateral coronary sinus. In a total of 23,300 coronary angiograms, 98 anomalous coronary arteries were detected (incidence 0.4%): 46 circumflex coronary arteries (47%), 25 right coronary arteries (25.5%), 10 left main coronary arteries (10.2%), three left anterior descending arteries (3.1%), six single coronary arteries (6.1%), and eight other anomalies (8.2%). The most frequent indication for angiography was angina (43.9%). The initial course of the anomalous coronary artery was not identified in 40.8% of cases. In two patients (2%), diagnostic imaging was used to identify the initial course. Associated atherosclerotic disease was present in 51% of patients. In addition, 18.4% had associated valvular disease, with the aortic valve being affected most often (15.2%). Some 16.3% of patients underwent treatment for the coronary anomaly. The incidence was similar to that observed in other published series, with anomalies in the circumflex coronary artery being diagnosed most frequently. Diagnostic imaging was underused.