Irregular menstruation is an important indicator of current and potential health problems. A woman's health is greatly influenced by her socioeconomic status. The purpose of this study was to examine the prevalence of irregular menstruation by socioeconomic status among South Korean women. Secondary data analyses were conducted among 4,709 women, aged 19-54 years, using raw data from the Korea National Health and Nutrition Examination Survey V (2010-2012), a nationally representative survey. Compared to women who graduated from university, the adjusted odds ratios (95% confidence intervals) for those who graduated from elementary school or lower, middle school, and high school were 3.256 (1.969-5.385), 2.857 (1.866-4.376), and 1.607 (1.261-2.048), respectively. Compared to women with a medium-high income level, the adjusted odds ratio (95% confidence interval) for women with the highest household income level was 1.409 (1.091-1.819). Irregular menstruation was prevalent among adult women and appeared to be associated with socioeconomic status, especially in terms of education and household income. This study's findings suggest that attention must be paid to women with low educational levels or high household incomes, to ensure early diagnosis and the provision of medical attention for irregular menstruation.