Purpose: This study was done to investigate the prevalence of suicidal ideation and associated factors in Korean adults. Methods: From the database of the 5th Korean National Health and Nutritional Examination Survey conducted in 2010, cross-sectional data for 6,283 adults (≥20 years) were used in this analysis. Results: One year prevalence of suicidal ideation was 14.8%. Higher suicidal ideation was found for women, elders, adults who were divorced or separated, who were in the lower socio-economic class, were alcohol dependent, had a short sleep time, and had higher perceived stress and depression. On stepwise multivariate logistic regression analysis, depression (odds ratio 6.89 [95% confidence interval 5.18~9.16]), perceived stress(3.52 [2.66~4.65]), being woman (1.72 [1.32~2.26]), being an elder (≥65 yrs) (1.78 [1.07~2.96]), low education(3.52 [2.66~4.62]) and not married (1.48 [1.04~2.12]) were associated with suicidal ideation in Korean adults. Conclusion: The results indicate that suicidal ideation is highly prevalent in Korean adults, especially in people with depression or high perceived stress. Identification of high-risk group and suicide prevention programs are warranted to reduce the prevalence of suicidal ideation.