BACKGROUND: Although postoperative back pain has been reported to occur, as a frequent complication of anesthesia and surgery, it is usually mild and self-limited. However, we experienced cases of uncontrolled postoperative back pain in patients even after IV-PCA administration. These patients' back pain was relieved by the traditional diclofenac sodium intramuscular injection, so we evaluated the efficacy of diclofenac sodium on uncontrolled postoperative back pain by IV-PCA. METHODS: We studied 16 patients who complained of postoperative back pain even with IV-PCA for postoperative pain control. When NRS pain score was above 5, the patients were treated with a diclofenac sodium 75 mg intramuscular injection. Postoperative back pain and operation site pain was measured by NRS before and after diclofenac sodium injection. RESULTS: There was a significant decrease in the pain score of postoperative back pain after diclofenac sodium injection without a dramatic improvement of operation site pain. CONCLUSIONS: Diclofenac sodium plays a useful role in the control of acute postoperative back pain.