Background: Unmet medical need which are indicators used globally to assess healthcare accessibility is a condition in which no satisfactory method of prevention, diagnosis, and treatment exists. The purpose of this study is to analyze factors related to unmet medical needs among Korean adults. Methods: We used a retrospective cross-sectional study design. This nationwide-based study included the data of 26,598 participants aged 19 years and older, obtained from the Korea National Health and Nutrition Examination Survey for 2013–2017. Using multiple logistic regression models, we analyzed the associations between factors that influence unmet medical needs and participants’ subgroups.Results: Despite Korea’s universal health-insurance system, we found that in 2017, 9.5% of Koreans experienced unmet needs. In the young adult group, men had a higher odds ratio of experiencing unmet medical needs compared to women (Males: OR = 1.83, 95% CI = 1.35-2.48; Females: OR = 1.42, 95% CI = 1.12-1.81). ). In particular, unlike men, women’s unmet medical needs increased as their incomes decreased (1Q OR = 1.55, 2Q OR =1.29, 3Q OR=1.26). Men and women showed a tendency to have more unmet medical needs with less exercise, worse subjective health state, worse pain, and a higher degree of depression.Conclusions: In conclusion, unmet medical needs contributing factors included having a low socioeconomic status, high stress, severe pain, or severe depression. Considering our findings, we suggest improving health-care access with low socioeconomic status.