To test the ability of ultra-high frequency ultrasound (13 MHz scanner) to distinguish between intact and ruptured ligaments on the lateral side of the ankle, we examined 20 patients with an acute inversion injury with MRI and ultrasound. When judged by the MRI diagnosis, an injured anterior talofibular ligament was correctly diagnosed by ultrasound in 13 of 14 and an intact anterior talofibular ligament in 5 of 6 patients. In the case of the calcaneofibular ligament, 4 ruptured and 16 intact ligaments were diagnosed equally well with both methods. The injured anterior tibiofibular ligament was correctly diagnosed by ultrasound in 6 of 9 patients, while the intact ligament was correctly recognized in 10 of 11 patients. Our findings indicate that it is possible to distinguish injured from intact ligaments sonographically.