Portable ultrasonography is increasingly used to evaluate ankle stability at the point of care. This study aims to determine the correlation of portable-ultrasonographic and fluoroscopic measurements of ankle laxity in a cadaveric ligament transection model of ankle ligament injury. We hypothesize that there is an association between portable-ultrasonographic and fluoroscopic measurements when performing stress evaluation of lateral ankle instability. Eight fresh-frozen below-knee amputated cadaveric specimens with intact proximal fibula underwent ultrasound and fluoroscopic evaluation of the ankle during anterior drawer and talar tilt testing. The assessment was first performed with all lateral ankle ligaments intact and thereafter with sequential transection of the anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament. The anterior drawer test was performed with both 50N and 80N of force, and talar tilt test was performed with 1.7 Nm of torque. Correlations between (1) portable-ultrasonographic and fluoroscopic measurements and (2) sequential transection of lateral ankle ligaments were evaluated using Spearman's rank correlations. The same statistical test was used to investigate the correlation between the ultrasonographic and the fluoroscopic measurements. The inter- and intra-observer agreement was assessed using the intraclass correlation coefficient through a two-way mixed-effects model with absolute agreement. Portable-ultrasonographic and fluoroscopic measurements increased as additional ligaments of the lateral ankle were transected (Spearman's rank correlation ranged from 0.74 to 0.81, 0.74 to 0.81, p-values < 0.001). Strong positive correlations between ultrasonographic and fluoroscopic measurements were found during the lateral ankle stability evaluation using anterior drawer and talar tilt testing (Spearman's rank correlation ranged from 0.81 to 0.85, 0.81 to 0.85, p-values < 0.001). Inter-rater (0.99, 95% CI:​ 0.98–0.99) and intra-rater reliability (0.97, 95% CI:​ 0.95–0.99) for the ultrasonographic measurements were substantial. In conclusion, there was a strong correlation found between ultrasonographic and fluoroscopic values measured during simulated anterior drawer and talar tilt test in a cadaveric ligament transection model. In this model, the portable-ultrasonographic measurement was found to be reliable for repeated measurements of the talar translation and the lateral clear space distance. Based on these data, ultrasonography is likely to become a valuable point of care diagnostic tool due to its ability to readily and dynamically evaluate suspected lateral ankle instability. Clinical Significance:​ The use of dynamic stress ultrasound to assess the anterior translation of the talus and the lateral clear space distance appears to be a reliable and repeatable technique to evaluate lateral ankle stability with a radiation-free, noninvasive, and low-cost manner.