Aim <p>The aim of this study was to examine the relationship between socio-demographic and lifestyle factors and multimorbidity among Thai adults.</p> Subject and methods <p>This cross-sectional study used data from 42,785 members of the Thai Cohort Study (TCS) in 2013 to identify risk factors associated with the prevalence of multimorbidity (coexistence of two or more chronic conditions). Multivariate logistic regression was applied to examine the correlation between socio-demographic and lifestyle elements and the prevalence of multimorbidity.</p> Results <p>The overall prevalence of multimorbidity was 10.3%. The highest prevalence was found in the capital, Bangkok, at 12.9%. The older the participant, the more likely they were to suffer from multimorbidity (p-trend = 0.0452). Moreover, participants who consumed more instant food (p-trend = 0.0446) and fast food (p-trend = 0.0313) were more likely to have multimorbidity. However, the more they exercised weekly, especially doing housework, the lower the odds of having multimorbidity (p-trend = 0.0034). Occasional or social drinking also reduced the odds of having multimorbidity compared to non-drinkers (adjusted odds ratio [AOR] = 0.80; 95% CI 0.70–0.95). Notably, excessive sleep (more than 8&#xa0;h, AOR = 1.29, 95% CI 1.07–1.55) or insufficient sleep (less than 6&#xa0;h, AOR = 1.24, 95% CI 1.09–1.41) may increase the odds of having multimorbidity.</p> Conclusion <p>The findings suggest that more attention should be paid to multimorbidity in the elderly. In addition, encouraging people to live a healthy life and engage in more exercise, such as household exercise, could be effective in reducing the likelihood of multimorbidity.</p>