The purpose of this study was to develop the Korean version of World Health Organization Quality of Life study assessment instrument (WHOQOL) and WHOQOL-BREF, an abbreviated version of WHOQOL and to identify contributing factors in the quality of life of Koreans. The WHOQOL and WHOQOL-BREF were translated into colloquial Korean according to instructions of the WHOQOL study group. Then the Korean questionnaire was applied to 538 subjects, composed of 171 medical patients and 367 healthy subjects who volunteered to rate the scale. Finally, 486 subjects completed the rating. Collected data were analyzed statistically. The Korean version of WHOQOL and WHOQOL-BREF domain scores demonstrated good test-retest reliability, internal consistency, criterion validity, content validity and discriminant validity. The physical, psychological, social and environmental domains made a significant contribution to explaining the variance in the quality of life while the independence and spiritual domains made a lesser contribution. The domain scores produced by the WHOQOL-BREF correlated highly with the WHOQOL. The physical health domain contributed most in overall quality of life, while the social domain made the least contribution. These results suggest that the Korean version of WHOQOL and WHOQOL-BREF are valid and reliable in the assessment of quality of life and that physical domain is contributing most and social and spiritual factors are contributing least to the quality of life in Koreans.