Atrial aneurysms are rare entities that can be congenital or acquired. Those involving the free wall or atrial appendage are even rarer. There are only 49 cases reported in the literature involving the left atrium and 8 in the right atrium until 2002. The most common clinical presentation is the appearance of recurring or incessant atrial arrhythmias. In addition, systemic embolization may occur as an imminent life-threatening event. We present the case of a female teenager who suffered from an embolic stroke during an atrial fibrillation. She had a giant aneurysm of the left atrial appendage that was successfully removed. Images from computed tomography, and of the aneurysm during the surgical intervention are shown.