BACKGROUND Due to the high prevalence of arterial hypertension and its role in the development of atherosclerosis, myocardial infarction and stroke, hypertension is a major public health challenge worldwide. There is limited knowledge of the prevalence of hypertension among seafarers who, however, are known to have an excess morbidity and mortality from these disorders. This article addresses the prevalence of hypertension among Danish seafarers and discusses potential risk factors for hypertension in maritime settings. METHODS A representative sample of 629 Danish seafarers who had statutory medical examinations was studied from the beginning of October 2011 to the end of June 2012. The medical examination included measurements of blood pressure. The prevalence of hypertension in the study population was stratified by age, work place on board, smoking status, alcohol intake, and body mass index. RESULTS The overall prevalence of hypertension in the study population was 44.7% (95% CI 40.8-48.6). In a comparison sample of adult Danes, the crude rate of hypertension was 12.6%. In addition, 41.8% (95% CI 38.0-45.7) of seafarers were pre-hypertensive. Hypertension was particularly increased among younger seafarers. The proportion of seafarers in antihypertensive treatment was low, in particular among the young seafarers. CONCLUSIONS Hypertension is a major health issue among Danish seafarers. In addition to ensuring antihypertensive treatment when needed, individual and collective prevention should address lifestyle issues as well as physical and psychosocial exposures at sea.