The authors recently observed two patients who suffered acute lower limb ischemia secondary to thrombosis of a small (diameter of less than 2 cm) popliteal artery aneurysm. A literature search lead to the conclusion that small popliteal aneurysms, covered with mural thrombus and presenting a distorted neck due to elongation, are prone to thrombosis. Another risk factor is a restrained outflow bed as a result of previous micro-embolisations into the tibial arteries. The authors conclude that small popliteal artery aneurysms are not so innocent as is often presumed.