Of the many evils that were inflicted upon the army of the West India Company in its years of activity in Brazil, few could be compared to diseases. However, there is little quantitative data in the field of historiography regarding the impact of disease on these troops. Apart from the limited amount of information about the diseases that affected many soldiers, little is known about the medical treatments that were available, the main diseases that affected the troops, and what were the causes. This article provides information to understand aspects that have been little studied in quantitative and systematic terms in the field of historiography, and demonstrates how the diseases afflicted the Company and affected its actions in the territory.