Coronary artery aneurysms are rare findings in patients referred for coronary angiography. Their prevalence ranges between 0.2% and 6% in different case series. We describe a male patient with a huge left main coronary artery aneurysm causing exertional angina, which was diagnosed with coronary angiography. All of the left coronary system arose from the aneurysm. He underwent coronary angiography again, followed by multislice computed tomography with a three-dimensional reconstruction. Although there is no known standard treatment modality for such aneurysms, we planned medical therapy after consultation with the cardiovascular surgery department. The patient's first visit was in March 2013, and he was thereafter followed up until September 2016.