The course of ulcer disease (UD) in sailors of the North seas was analysed and compared to that in non-sailors. UD in sailors runs with less pronounced subjective symptoms, manifests at younger age, is frequently accompanied by duodenal mucosa erosions and duodenogastric reflux. The greatest number of UD exacerbations was observed in the first month in sea and two months after getting home. Because of the fear to lose the job the sailors often do not seek medical assistance in spite of ulcer symptoms and this results in many cases of late diagnosis.