The goal of this study was to evaluate the reliability and validity of the Korean version of the Brief Fatigue Inventory (BFI-K). One hundred seventy-eight cancer patients and the same number of age- and sex-matched control subjects completed the BFI-K, the European Organization for Research and Treatment of Cancer QLQ-C30 (EORTC QLQ-C30), the Beck Depression Inventory (BDI), and a Brief Pain Inventory (BPI). The Cronbach's alpha coefficient for the BFI-K was 0.956 in the cancer patient group and 0.955 in the control group. The global score and nine of the single item scores for the BFI-K were significantly correlated with the fatigue and global health status/QoL subscale of the EORTC QLQ-C30, BDI, and BPI (coefficient range 0.38-0.66). Discriminant validity showed that BFI-K could distinguish significant differences of performance status between subgroups of patients, and between the cancer patient group and the control group, as expected. Our study has shown that the BFI-K is a reliable, valid self-rating instrument in terms of its psychometric properties.