Since its introduction in 1977, the number of PTCAs and its indications have grown. Along with more frequent usage, newer complications have been reported. Aneurysm of left main coronary artery is rare. This report describes the formation of a new non-obstructing aneurysm in the left main coronary artery after PTCA of left circumflex artery. The patient has had 7 yr of follow-up with a benign clinical course.