Background: Refugees are forced migrants but there is a large variation in the distance that refugees cover and there is a knowledge gap on how this may affect refugee' health and health care needs. We investigated the association between long-distance migration and post-traumatic stress disorder (PTSD), a serious psychiatric disorder associated with deteriorating mental and somatic health. Methods: Included from 2016-2019 were 712 adult Syrian refugees and asylum seekers in Lebanon and Denmark arrived up to 12 months prior. PTSD was assessed using the Harvard Trauma Questionnaire and the estimate of association was obtained by multiply imputing missing data and adjusting for confounding by propensity score-weighting with covariates age, sex, socioeconomic status, trauma experience and WHO-5-score, reporting the bootstrap 95-percentile confidence interval (95% CI). Additionally, a number of sensitivity analyses were performed. Results: After multiply imputing missing data and propensity score-weighted adjustment for confounding, migration to Denmark instead of Lebanon was associated with an increase in PTSD prevalence of 9 percentage point (95% CI [-1; 19] percentage point). Discussion: We found that long-distance migration was associated with an increase in the prevalence of PTSD suggesting that long-distance migration may be a factor to consider when assessing refugees' and asylum seekers' health. To secure timely and appropriate health care for this vulnerable group we need to remedy the current knowledge gap regarding the health effects of migration. This study is the first step in doing so.