Purpose: In this study, we measured the serum interleukin-8 (IL-8) levels in patients with hepatocellular carcinoma (HCC) to evaluate its correlation with clinicopathological features and prognosis. Experimental Design: ELISA was used to detect the concentrations of IL-8, vascular endothelial growth factor, and macrophage migration inhibitory factor in preoperative sera of 59 patients with resection of HCC and 15 healthy subjects. Results: Preoperative serum IL-8 was found to be significantly elevated in patients with HCC compared with healthy subjects (median, 17.6 versus 1.0 pg/ml, P = 0.046). The levels of IL-8 correlated significantly with a large tumor size (>5 cm), absence of tumor capsule, presence of venous invasion, and advanced pathological tumor-node-metastasis stage. Serum IL-8 level was a significant prognostic factor in terms of disease-free and overall survival. Patients with a serum IL-8 level of >17.6 pg/ml had a poorer disease-free survival than those with a level of <17.6 pg/ml (median disease-free survival 4.7 versus 19.2 months). Multivariate analyses showed that serum IL-8 level was a significant and independent prognostic factor of survival. Conclusions: Significant correlations of serum IL-8 levels with tumor size and tumor stage suggest that IL-8 may be directly or indirectly involved in the progression of HCC. These findings indicate that serum IL-8 may be a useful biological marker of tumor invasiveness and an independent prognostic factor for patients with HCC.