STUDY DESIGN: This is a prospective study. OBJECTIVES: To evaluate the effects and complications of patient controlled analgesia(PCA) after spinal fusion. SUMMARY OF LITERATURE REVIEW: Spinal fusion was associated with highest pain and dosage of analgesics among the orthopedic procedures due to the nature of its procedure. Higher requirement of analgesics might cause several postoperative complications including severe respiratory depression and death. It is well known that PCA provides better pain relief and lower complications than as needed intramuscular analgesia. MATERIALS AND METHODS: We compaired the efficacy and possible side effects of intravenous PCA(n = 24) with control(n = 13) in patients undergone spinal fusion. The degree of resting pain, movement pain, and side effects were marked by the patients with 100mm visual analog scales. RESULTS: Postoperative pain control with intravenous PCA showed more effective analgesia and higher patient's satisfaction without causing significant side effects. CONCLUSIONS: Intravenous PCA in patients undergone spinal fusion was effective therapeutic modality in the aspect of pain relief, complications, and satisfaction rate. PCA will be a good alternative for as needed intramuscular analgesia after spinal fusion.