There have been major developments in the understanding of disease and its treatment in the last 150 years. The development of the knowledge base on patterns of disease and injury in seafarers and on the effectiveness of intervention to prevent and treat them indicates the sorts of information that were collected and the settings in which it was possible to collect it. They also show how it has been used, as well as the reactions of those in the maritime sector to the collection and analysis of health information and to its use as a means of reducing harm.