To assess whether ultrasound-guided percutaneous acetic acid injection is superior to percutaneous ethanol injection in the treatment of small hepatocellular carcinoma (HCC), 60 patients with one to four HCCs smaller than 3 cm were entered onto a randomized controlled trial. Thirty-one and 29 patients, respectively, were treated by percutaneous acetic acid injection using 50% acetic acid or by percutaneous ethanol injection using absolute ethanol. There were no significant differences in age, sex ratio, Child-Pugh class, size of tumors, or number of tumors between the two groups. When there was no evidence of viable HCC from biopsy, plain and helical dynamic computed tomography, or angiography, the treatment was considered successful and was discontinued. All original tumors were treated successfully by either therapy. However, 8% of 38 tumors treated with percutaneous acetic acid injection and 37% of 35 tumors treated with percutaneous ethanol injection developed a local recurrence (P < .001) during the follow-up periods of 29 +/- 8 months and 23 +/- 10 months, respectively. The 1- and 2-year survival rates were 100% and 92% in percutaneous acetic acid injection and 83% and 63% in percutaneous ethanol injection (P = .0017). A multivariate analysis of prognostic factors revealed that treatment was an independent predictor of survival. The risk ratio of percutaneous acetic acid injection versus percutaneous ethanol injection was 0.120 (range, 0.027-0.528; P = .0050). In conclusion, percutaneous acetic acid injection is superior to percutaneous ethanol injection in the treatment of small HCC.