Ankle injuries involving the lateral ankle ligaments are among the most common injuries of the musculoskeletal system. Ankle ligament injuries are collectively known as ankle sprains, which refer to the mechanism of the injury rather than the degree of the injury. Diagnostic accuracy of complete lateral ligaments rupture with an acute instability of the ankle joint (grade III) and ligaments laxity in adults with the chronic ankle instability is problematic. Stress ultrasonography can image the lateral talocrural joint and evaluate acute or chronic lateral ankle instability. Purpose: The aim of this study was to investigate the result of ultrasound diagnostics of lateral ankle instability in held-forced positions (anterior drawer test). Methods: 20 patients were examined after acute lateral ankle sprain (grade III) under local anesthesia. 20 patients were examined with chronic ankle instability symptoms. Diagnosis of acute ankle instability and chronic mechanical ankle instability was based on musculoskeletal ultrasound examinations. The distance between the posterior rim of the tibia and talus was measured for each ankle. To diagnose the ligament tear as being a complete tear, the difference between the injured and uninjured ankle had to be greater than 3 mm in dorsal cuts (Ernst approach to identify talocrural instability). Results: Ultrasound examinations performed under local anesthesia with ankles in held-forced positions (anterior drawer test) demonstrated that the difference between the injured and uninjured ankle was greater than 3 mm in dorsal cuts. We found no significant differences in talocrural joint laxity between acute and chronic ankle instability. Conclusion: Stress ultrasonography in acute and chronic ankle instability identified significant differences in non-stress (basic neutral position) and stress position (anterior drawer test). Incomplete healing of the ligament tissue results in post-traumatic ligament laxity, predisposing the joint to further injury. Ultrasound imaging represents an effective, non-invasive and relatively low-cost method without negative side effects, which makes the ultrasound scanner a practical tool in the clinical setting.