We report a case of stress fracture of the clavicle in which diagnosis was delayed due to the unusual localization of pain and absence of predisposing risk factors. A 34-year-old woman presented with severe right-sided pain in the shoulder, arm, neck, and hemithorax, and numbness in her right upper extremity. Systemic radiographs, cervical and brachial plexus magnetic resonance imaging (MRI) and thorax computed tomography (CT) did not show any pathology. In a retrospective review of the shoulder MRI sections, an edematous appearance was noted in the right clavicle and adjacent soft tissues, suggesting a stress fracture of the clavicle. The patient was followed-up with activity limitation and analgesic treatment and her complaints subsided gradually. Control radiographs obtained 10 months later showed fracture healing with atypical callus formation. Stress fractures of the clavicle must be kept in mind in the differential diagnosis of shoulder pain presenting as an atypical severe arm pain radiating to the upper extremity and hemithorax. In suspected cases, it may be helpful to obtain CT and MRI sections parallel to the long axis of the clavicle.