BACKGROUND: Although hemorrhoids are one of the most common anal diseases among Koreans, risk factors for hemorrhoids have not been well identified. METHODS: We analyzed the data from the 4th Korean National Health and Nutrition Examination Survey (KNHANES) between 2007 and 2009. Study subjects were 17,228 participants of KNHANES who were aged 19 years or older. Logistic regression analysis was conducted to evaluate associations between hemorrhoids and probable risk factors. RESULTS: Overall prevalence of hemorrhoids among study subjects was 14.4%, being more prevalent among women (15.7%) than among men (13.0%). Obesity and abdominal obesity were associated with a higher risk of hemorrhoids with odds ratio (OR) (95% confidence intervals, 95% CI) of 1.13 (1.01 to 1.26) and 1.16 (1.04 to 1.30), respectively. Both self-reported depression (OR, 1.83; 95% CI, 1.62 to 2.08) and physician diagnosed depression (OR, 1.71; 95% CI, 1.35 to 2.17) were associated with significantly higher risk of hemorrhoids. No regular walking (OR, 1.11; 95% CI, 1.00 to 1.23) and experience of pregnancy (OR, 1.62; 95% CI, 1.17 to 2.25) for women were also associated with higher risk of hemorrhoids. However, educational level, alcohol consumption, physical activities, diabetes mellitus, hypertension, fiber, fat intake, and energy intake were not associated with a risk of hemorrhoids. Low quality of life assessed with EuroQol-5 Dimension and EuroQol-Visual Analogue Scale was significantly associated with hemorrhoids. CONCLUSION: This nationwide cross-sectional study of Korean adults suggests that obesity, abdominal obesity, depression, and past pregnancy may be risk factors for hemorrhoids and hemorrhoids affect quality of life negatively.