Purpose <p>This study aimed to examine the association between electronic cigarette (e-cigarette) use and sleep quality among Korean adults, taking into account various smoking behaviors and cumulative exposure.</p> Methods <p>Data were drawn from the 2018 Korea Community Health Survey (KCHS), a nationally representative dataset. A total of 159,505 participants aged ≥ 19 years were included. Sleep quality was measured using the Korean version of the Pittsburgh Sleep Quality Index (PSQI). Smoking behavior was classified into five groups: dual users, exclusive e-cigarette users, conventional cigarette smokers, former smokers, and never smokers. Multivariable logistic regression analysis was performed to assess the association between smoking behavior and poor sleep quality (PSQI &gt; 5), adjusting for demographic, socioeconomic, and health-related variables. Sensitivity analyses accounted for cumulative exposure using pack-years of smoking.</p> Results <p>Overall, 34.2% of participants were identified as poor sleepers. Compared with never smokers, the odds of poor sleep were significantly higher among former smokers (adjusted odd ratio [AOR] = 1.21), conventional cigarette smokers (AOR = 1.33), e-cigarette users (AOR = 1.73), and dual users (AOR = 1.75). These associations remained consistent after adjustment for cumulative exposure measured by pack-years. However, pack-years alone was not a significant predictor of poor sleep quality.</p> Conclusion <p>E-cigarette use—both exclusive and dual use—is significantly associated with poor sleep quality, independent of conventional smoking history and cumulative exposure. Addressing smoking behaviors may be beneficial for individuals experiencing sleep difficulties. Longitudinal studies are warranted to establish causal relationships and guide public health interventions.</p>