This study evaluates 76 cases of shoulder instability in dogs, functional outcome after treatment, and the effectiveness of medial biceps tendon transposition using a metallic staple. Clinical examinations of the shoulder were performed and radiographs were taken. Conservative treatment or surgery (biceps tendon transposition or arthrodesis) was then opted for on the basis of type of instability, associated lesions and dog (age, weight, behaviour). Long-term functional outcome was categorized as 'excellent', 'good', 'average' or 'poor'. In our series, the most frequently affected breed was the Poodle (13%). Humeral head intermittent displacement was either medial (80%), lateral (19%) or cranial (1%). On clinical examination, 97% of the animals experienced pain. In anaesthetised dogs, shoulder instability was observed in 90% of the population. Muscle atrophy (33%) and associated radiographic lesions (34%) were less frequent. Ninety-five percent of the dogs were treated surgically, either by bicipital tendon transposition (81%) or by shoulder arthrodesis (19%). Results were 'good' to 'excellent' in 25% of the animals treated conservatively, and in 84.5% and 87.5%, respectively, in those treated by tendon transposition and arthrodesis. Complications did not arise from the use of a metallic staple to anchor the tendon during medial transposition. Tendon transposition or arthrodesis resulted in a good functional outcome in more than 80% of the dogs with shoulder instability. During the medial transposition, the biceps tendon was easily and effectively stabilized using a metallic staple.