Obstetric brachial plexus palsy (OBPP) refers to upper limb paralysis secondary to a sustained traction or compression injury to the brachial plexus during birth. The reported incidence in developed countries is 2 per 1000 live births. The assessment and planning of appropriate treatment is important in the early stages of OBPP. The aim of our study was to examine the relationship between the range of motion and upper extremity function of the shoulder in patients with OBPP who were treated by tendon transfer. This study included 48 patients who had shoulder tendon transfer at least 6 months ago in Istanbul Medical Faculty, Department of Plastic and Reconstructive Surgery, Department of Surgery of the Hand. Range of motion measurements were performed using a universal goniometer and the modified mallet classification was used to categorize global shoulder function. Pediatric evaluation of disability inventory (PEDI) and Canadian occupational performance measure (COPM) were used to evaluate functional ability, activity and participation. When examining relationships between range of motion and functional scores, there was a statistically significant relationship between COPMP score and external rotation, and no relationship was found between other motion functional scores. The study demonstrated that, the use of the pattern of development and motivation of patients to participate is also important among range of motion and muscle strength for upper extremity function.