The evaluation of 98 pseudoarthroses of the shaft of the humerus showed that 42 of these occurred after conservative and 56 after surgical treatment of the original fracture. It appears that pseudoarthroses are caused in conservative treatment chiefly by the traction methods. Among the surgical methods, intramedullary nailing does not seem to bring about sufficient stabilization with a satisfactory measure of safety, whereas in the case of plate osteosynthesis, errors in respect of operation technique are mainly responsible for causing pseudoarthroses. All 98 pseudoarthroses returned to normal condition after proper plate osteosynthesis and, if necessary additional deposition of cancellous bone graft.