Introduction: Foot and ankle injuries (FAI) are very common, with about 6000 cases per day in France. Unlike lateral ankle sprain (LAS), the diagnosis of midtarsal joint sprain (MJS, also known as Chopart's joint sprain) is not widely known. This prospective study aims to detail the epidemiology of MJS and compare it to LAS. Patients and method: The study was conducted within our institution over a period of 16 months. Patients with clinical signs predictive of MJS without radiographic bone lesion underwent ultrasound assessment. MJS was diagnosed in case of at least 1 lesion of the dorsal midtarsal joint ligaments. Results: A total of 2412 patients consulted for FAI; 188 had clinical and radiographic criteria for ultrasound examination. Eighty-two cases of MJS were diagnosed (3.4% of FAIs). Sports injuries were more frequent in MJS (P=0.04), and mechanisms more varied than in LAS, with inversion injury in 75% of cases and plantar hyperflexion in 22%. Sprain was severe in 70% of cases, with complete ligament tear. Clinical and ultrasound analyses correlated in only 40% of cases of MJS, versus 98% for LAS. Conclusion: MJS is frequent, difficult to diagnose clinically, and often severe. Clinical presentation and injury mechanisms differ from ankle sprain. Ultrasound seems to be an indispensable tool in diagnosis. (C) 2016 Elsevier Masson SAS. All rights reserved.