This study evaluated the Korean version of the EORTC QLQ-C30 (version 3.0) in terms of psychometric properties and its validation. One hundred and seventy patients completed three questionnaires EORTC QLQ-C30, the Beck depression inventory (BDI), and a brief pain inventory (BPI). Multitrait scaling analyses demonstrated that all scales met multidimensional conceptualization criteria, in terms of convergence and discrimination validity. Cronbach's alpha coefficients for eight multiple-item scales were greater than 0.70, with the exception of cognitive functioning. All interscale correlations were statistically significant in the expected direction (p < 0.01). Multivariate analyses showed that physical and emotional functioning were significant explanatory variables for the global quality-of-life (QOL) scale (regression coefficients: 0.36, p < 0.001; and 0.37, p < 0.001; respectively). All scales were significantly associated with pain severity and interference of the BPI, and with the cognitive-affective and somatic scales of the BDI. The emotional-functioning scale was substantially correlated with the cognitive-affective scale and somatic scale of the BDI. These results demonstrate that the Korean version of the EORTC QLQ-C30 is a valid instrument for evaluating Korean-speaking patients with cancer, and can be used to distinguish clearly between subgroups of patients of differing performance status.