The long-term postoperative clinical courses were evaluated in 40 patients who underwent trans-peritoneal anterior discectomy and interbody fusion at our institution from 1955 through 1959. Thirty-four out of forty patients were followed up by physical and radiological examinations, and six by telephone interview. All subjects have been evaluated at least every 10 years after surgery. The results were as follows: 1) Thirty-four of forty (85%) patients were rated as satisfactory after a minimum 30-year follow-up. 2) Deterioration of the clinical course was probably attributable to age-related physical weakness. 3) The clinical results in the one-level fusion group were better than those in the two-level fusion group. 4) In the L4/5 fusion group, the adjacent disc degeneration was noted especially at the L3/4 level. Narrowing of the L3/4 disc was observed around 15 years after surgery irrespective of the patient ages at the time of follow-up examination. 5) In the L4/5 fusion group, the clinically significant X-ray findings included disc space narrowing, posterior olisthy, and horizontal displacement at the adjacent cranial level.