Most smokers who use electronic cigarettes (e-cigarettes) to stop smoking simultaneously use conventional cigarettes (dual users). We aimed to compare the prevalence of cardiovascular risk factors among dual users, cigarette-only smokers, and never smokers in Korean men. We used data acquired from Korean National Health and Nutrition Examination Survey (2013-2017) pertaining to 7,505 male participants aged 19 years or older. About 85% of e-cigarette users were dual users. Dual users had greater nicotine dependence and higher urinary cotinine levels than cigarette-only smokers. Dual users had more psychosocial and behavioural risk factors, including perceived high stress, depressive mood, high daily intake of energy, and obesity, than never smokers and cigarette-only smokers. The prevalence of metabolic syndrome (MetS) was higher among dual users, and their multivariate-adjusted prevalence odds ratio for MetS was 2.79 (P < 0.001) compared with never smokers and 1.57 (P = 0.038) compared with cigarette-only smokers. Given that most e-cigarette users are dual users and dual users are more vulnerable to cardiovascular risk factors than cigarette-only smokers and never smokers, more active treatment for smoking cessation and intensive lifestyle interventions for dual users should be considered with priority.