Introduction: Sprained ankle is a very common injury in children. Proper treatment of ligament injuries enables full recovery. X-ray and US examinations are commonly available diagnostic methods. Material and methods: Two hundred and six children (113 girls and 93 boys, mean age 10.6) with recent ankle joint sprain (up to 7 days of injury) were subject to a retrospective analysis. All patients underwent an X-ray and US examination of the ankle joint within 7 days of injury. In 19 patients, anterior talofibular ligament reconstruction was conducted. Results: X-ray failed to visualize a pathology in 129 children (63%); in 24 patients (12%), avulsion fracture of the lateral malleolus was found, and in 36 cases (17%), effusion in the talocrural joint was detected. Ultrasonography failed to visualize a pathology in 19 children (9%); in 60 patients (29%), it showed avulsion fracture of the lateral malleolus involving the attachment of the anterior talofibular ligament (ATFL); in 34 cases (17%), complete ATFL tear was detected, and in 51 patients (25%), partial ATFL injury was found. Other injuries constituted 19%. The surgeries conducted to repair the anterior talofibular ligament (19) confirmed the US/X-ray diagnoses in 100% of cases. Avulsion ATFL injury, i.e. the one that involves the ligament attachment site, is usually found in younger children (median: 8 years of age). Complete ATFL tears (not involving the attachment site) concern older children (median: 14 years of age). Conclusions: Since X-ray is of limited value in diagnosing ankle joint pathologies in recent sprain injuries in children, soft tissue imaging, i.e. ultrasonography, is the basic examination to assess the ligament complex. Avulsion fractures, which involve the ATFL attachment site and are usually found in younger children, are a consequence of the incomplete ossification and require urgent diagnosis and orthopedic consultation.