The association between the overexpression of aspartyl-(asparaginyl)- β-hydroxylase (AAH) and the invasiveness of hepatocellular carcinoma (HCC) in vitro has been reported. However, the prognostic value of AAH expression in HCC remains unclear. The purpose of this study was to investigate the relationship between AAH expression, tumor recurrence, and patient survival. We identified AAH as the most overexpressed gene in HCC by way of complementary DNA microarray hybridization. A prospective study of 233 patients undergoing curative resection indicated that AAH expression was an independent factor affecting recurrence (hazard ratio [HR] 3.161, 95% confidence interval [CI] 2.115-4.724, P < 0.001) and survival (HR 2.712, 95% CI 1.734-4.241, P < 0.001). Patients with AAH overexpression had a poorer prognosis than those with AAH underexpression (P < 0.001 for both recurrence and survival). In Barcelona Clinic Liver Cancer stage A patients with AAH overexpression or underexpression, the tumor recurrence and survival rates were also statistically different (45% and 85% versus16% and 33% in 1- and 3-year cumulative recurrence rates, respectively; 73% and 37% versus 90% and 80% in 1- and 3-year survival rates, respectively; P < 0.001 for both). Furthermore, in stage A patients with tumors measuring ≤5 cm in diameter, the time to recurrence was 26.7 ± 1.6 versus 51.9 ± 2.8 months, and the 1- and 3-year survival rates were 97% and 52% versus 100% and 90% in AAH overexpression and underexpression patients, respectively (P < 0.001 for both). Conclusion: AAH overexpression in HCC is strongly correlated with worse surgical outcome, and this molecule likely provides a more precise prognostic predictor in early stage HCCs. Copyright © 2010 by the American Association for the Study of Liver Diseases.