BackgroundOn merchant ships, the medical treatment including emergency interventions on the high seas are carried out by nautical officers who have to pass a forty hours medical refresher course every five years in order to meet international requirements. This study aims to show the most frequent kinds of medical emergencies on the high seas and to assess the seafarers’ knowledge about their treatment.Methods465 nautical officers who participated in the medical refresher course at the Institute for Occupational and Maritime Medicine in Hamburg, within the period from 2006 to 2013, were interviewed about their experience of serious diseases and accidents on board, which had led to an emergency port call, a course deviation or an evacuation. Furthermore, prior to the course the officers were asked to answer 18 basic medical questions about common medical issues on board.Results133 seafarers (28.6%) reported that they had been confronted with at least one serious medical emergency at sea. These emergencies encompassed trauma (37.9%), cardiovascular diseases (18.2%), severe gastrointestinal diseases (15.9%), serious skin or pulmonary infections (9.8%), neurological (9.1%) and urological diseases (4.5%) as well as burns (4.5%). With regards to the basic medical questions, an average of 70.7% of the total score had been achieved (from 26.8% to 100%). On average, 65.5% of internal and 65.6% of surgical questions had been answered correctly. Proper answers to toxicological and infectious questions had been given by 93.3% and 94.1% respectively and to topics of hypothermia and medical treatment by 59.4% and 61.0%. In total, a significant number of younger seafarers answered the questions correctly (p = 0.001).ConclusionsAccording to this study, serious emergencies on board are most frequently related to trauma or cardiovascular diseases. Taking into account the acquired medical knowledge, there seems to be a need to train deck officers within these fields more intensively. Considering the knowledge of seafarers about medical issues directly before attending their medical refresher course, the 5 years interval without any form of refresher course appears to be too long to guarantee adequate medical treatment by the lay persons on board.