Pseudoaneurysm of the inferior lateral genicular artery occurred in a 25-year-old man after arthroscopy. The arthroscopy was not complicated by postoperative bleeding or hemarthrosis, which has been associated with pseudoaneurysm formation. The diagnosis was confirmed on 99mTc radionuclide scanning and ultrasound, and the anatomy was demonstrated by digital subtraction angiography. Exploration and excision were performed without complication or recurrence. There are several methods for investigating these rare lesions.