BACKGROUND: Previous studies have shown that self-reports tend to underestimate smoking status, especially among women in Korea. We therefore assessed the characteristics of Korean women smokers who falsely described themselves as non-smokers. METHODS: The subjects were 4,135 adult women aged > or =19 years who participated in the 2008 Korean National Health and Nutrition Examination Survey. Of these, 3,151 subjects answered questions about their smoking status on self-reported questionnaires and underwent assays of urinary cotinine concentration. Subgroups of false respondents (n = 131) and true respondents (n = 198) regarding smoking were determined by comparing their responses on questionnaires with their urinary cotinine levels. RESULTS: Among adult Korean women, the self-reported smoking rate was 7.4% (95% confidence interval [CI], 6.4% to 8.4%); however, using urinary cotinine >100 ng/mL as a marker of smoking, the smoking rate was 11.8% (95% CI, 10.5% to 13.3%). In multivariate analysis, after adjusting for type of household, family income, and suicidal ideation, the odds ratios (ORs) of false respondents were 3.49 (95% CI, 1.41 to 8.63) for college-educated women and 2.47 (95% CI, 1.22 to 5.01) for women with high school education, relative to women with elementary school education. Married women with living spouses (OR, 2.80; 95% CI, 1.33 to 5.90) were more likely to respond falsely than unmarried women. Women who reported trying to reduce weight within 1 year (OR, 2.70; 95% CI, 1.47 to 4.93) and those who reported being less stressed (OR, 1.82; 95% CI, 1.08 to 3.07) were more likely to be false respondents. CONCLUSION: The smoking rate determined using urinary cotinine concentration was higher than the self-reported rate among Korean women. Among smokers, those who were more educated, married, living with a husband, trying to reduce weight, and less stressed tended to describe themselves falsely as non-smokers.