In children and adolescents with chest pain and dyspnea, pneumonia, pleural effusion, and empyema are the frequent causes in the differential diagnosis. Malignant tumors of the chest wall are rare and most originate from the ribs. In children, the most frequent malignant tumor of the rib is Ewing's sarcoma. Osteosarcomas of the rib are very rare. Osteosarcoma has a predilection for rapidly growing long bones including the femur, tibia and humerus in adolescents. In this paper, we present an adolescent girl who presented with chest pain and dyspnea with osteosarcoma that originated from the rib and extended to the right hemithorax.