This study examines the variation patterns of Korean male immigrants' mental health in relation to their length of residence in the United States and identifies significant factors related to the variations. The main hypothesis suggests two critical stages in which Korean immigrants' mental health would become highly vulnerable--the early exigency stage (1-2 years after immigration) and the later marginality stage (11-15 years after immigration). Hence, the hypothesis predicts a curvilinear (the inverted J-curve) relationship between length of residence and life satisfaction. This hypothesis is tested through an epidemiological survey of 334 Korean male immigrants (20 years and older) in the Chicago area. Results of data analyses generally confirm the hypothesis: 1) the immigrants' mental health is most highly vulnerable at the early exigency stage, 2) the degree of their mental well-being generally increases with length of residence, 3) the rate of increase in mental well-being tends to stagnate after the resolution stage, confirming the inverted J-curve hypothesis and 4) job satisfaction is the most significant variable accounting for the mental health patterns of the Korean male immigrants. Theoretical and methodological implications of the findings are discussed in the conclusion.