We reviewed clinically the 56 patients, who had anterior interbody fusion of the cervical spine due to various causes, from 1975 to 1984. The result of the studies are as follows; 1. Inawaisting sign of the grafted level is the one of the most important prognostic factors which indicates the favorable fusion. 2. The mechanism of the inwaisting sign is not confirmed, however plausible explanation is the flexure drift law, which cause the inwaisting phenomena. 3. The time of clinical, radiological union and the appearance of the inwaisting sign of the grafted bone in the fusion of the lower cervical spine are displayed earlier than in the upper cervical spine. 4. Fusion at the one level is obtained one or two weeks earlier than the two level fusion. At the two level fusion, one large bone block operation achieved the earlier bony union than the two separate bone blocks fusion; it could shorten the fusion time by 4 weeks radiologically, although there were no significant difference in clinical aspect and inwaisting sign. 5. In the anterior interbody fusion of the cervical spine, clinical fusion took place in 6–7 weeks, and radiological one in 10-14 weeks after the fusion operation. And it was not influenced by the type of injury or neurological complications. The inwaisting sign appeared from the 4th to 7th week postoperatively. 6. There are no problems in the case of posterior instability initially. The reason is that we have performed the cervical traction and absolute bed rest for 4 to 6 weeks before the anterior interbody fusion in order to take the healing of the poterior ligament complex.