We treated 43 acute tears of the calcaneofibular ligament by operation in 43 patients after subtalar arthrography. There were 22 men and 21 women with a mean age of 22.3 years (14 to 61). Anteroposterior (AP), lateral and oblique views were obtained with the foot in 45° of internal rotation and the ankle in the neutral position. Any communication or leakage to the ankle, tendon sheaths, subcutaneous tissue and sinus tarsi was recorded. We examined an oblique view of the microrecess along the interosseous ligament and an AP view of the lateral recess just under the distal end of the fibula. We also studied a control group of 27 patients with isolated injuries of the anterior talofibular ligament without rupture of the calcaneofibular ligament. The findings in the two groups were significantly different when examined for leakage to the ankle (p = 0.0002), to the peroneal tendon sheaths (p = 0.0347) and to the subcutaneous tissue (p = 0.0222), absence of the microrecess (p = 0.0055) and presence of the lateral recess (p = 0.0012). Many ankle sprains which involve tearing of the calcaneofibular ligament are accompanied by injuries of the subtalar joint. Combined injuries of the anterior talofibular ligament and calcaneofibular ligament, and isolated injury of the anterior talofibular ligament should be differentiated