Due to nature of their profession, seafarers visit many ports in different parts of the world and are thus exposed to various infectious diseases. And yet, chronic non-communicable diseases, malignant illnesses and accidents have lately become an important cause of death among the seafarers. Although before the COVID-19 pandemic outbreak the communicable disease outbreaks were becoming less common, their share in seafarer morbidity remains significant. The aim of this research is to determine the most common infectious risks/contagious diseases on ships. The Medline and Scopus databases have been searched using the following key words: seafarers, infectious diseases, morbidity, mortality. The information sources include relevant literature, as well as national and international regulations on preventive measures against infectious diseases. At the global level no national or international surveillance systems exist on infectious disease occurrences on ships. There are only a few exceptions. However, based on some available individual and group research, conclusions may be drawn concerning the most important diseases in seafarer pathology. Of communicable/infectious diseases on ships, the most important ones are the acute respiratory illnesses, including the COVID-19 disease, followed by food poisoning/acute gastroenteritis, vector-borne diseases and HIV as the most common sexually transmitted disease in the past 20 years. Estimating the threat from infectious diseases in seafarers depends on the type and trade of vessels. For COVID 19 and other respiratory infections, as well as food poisoning, risks are higher on cruise ships and passenger ships than on cargo ships. For better understanding of the issue, we need internationally co-ordinated studies and well organised surveillance systems.