CD98 has been associated with tumor growth and is highly expressed in human neoplasms. The aim of this study was to evaluate the clinicopathological significance of CD98 expression in thymic epithelial tumors. Forty-nine patients with thymic epithelial tumors were included in this study. Tumor sections were stained by immunohistochemistry for CD98; vascular endothelial growth factor (VEGF); micro-vessels (CD31 and CD34); cell cycle control marker (p53); and apoptosis marker (Bcl-2). CD98 expression for low-risk thymomas, high-risk thymomas, and thymic carcinomas were 1 (4%) of 27, 9 (82%) of 11, and 11 (100%) of 11, respectively. There was positive correlation between CD98 and VEGF (p<0.001), microvessel density (CD31 and CD34) (p<0.001) and p53 (p<0.001). However, Bcl-2 showed no positive correlation with CD98 expression. The expression of CD98 were also significantly associated with the grade of malignancy in thymic epithelial tumors. Multivariate analysis revealed that overexpression of CD98 was a significant independent factor predicting a poor outcome in thymic epithelial tumors. CD98 expression was associated with the grade of malignancy in thymic epithelial tumors. Moreover, CD98 expression was closely correlated with angiogenesis and cell cycle control, and was useful for predicting poor outcome.