We investigated the ultrasonographic (US) features of Stener injury and thus the role of US in the diagnosis of this condition. Stener injuries are characterized by the tear of the cubital ligament system of the first metacarpophalangeal joint during hyperabduction. This condition may be associated with the displacement of the ligament proximal stump above the thumb adductor muscle. We examined 12 patients (9 men and 3 women) with a clinical diagnosis of joint instability due to hyperabduction of the first metacarpophalangeal joint. All the US exams were performed with a linear probe (7.5-10 MHz); a 13-MHz probe was also used in 7 patients. All the patients were submitted to radiography in the standard projections, to detect associated bone injuries. US allowed the identification of a round lesion surrounded by a hypoechoic halo, between the distal edge of the dorsal interosseous muscle of the first finger and the first metacarpal bone (the proper Stener injury) in 4/12 patients. In contrast, no typical sign was shown in the other 8 patients. US results were then compared with surgical findings. The diagnosis of proper Stener injury was surgically confirmed in 4 patients. Only 2 patients with clinical signs of thumb instability, who were negative for Stener injuries at US, were submitted to surgery which demonstrated the ligament tear responsible for joint instability, but ruled out the displacement. To conclude, US must be integrated with clinical signs because this imaging method accurately shows complete tears with displaced proximal stump of the cubital ligament.