This article investigates the relationship between the debates in Belgium about the climate and the so-called health or insalubrity of the Congo, and the political agendas of the contributors to these debates in the period between the start of the Leopoldian exploration of Central Africa in 1876 and the annexation of the Congo Free State by Belgium in 1908. From the very beginning of this exploration, attention was focused on the climate. For example, meteorological data about the explored and annexed regions were collected and the climate was often represented as an unknown evil : it was seen as extremely unhealthy. Stories of success as well as of terrible misfortune produced by other imperial powers about experiences in similar regions, influenced the way climate was perceived. For the defenders of the imperial project, who wanted to promote the Congo as a lucrative and healthy region, it was important to combat the idea of a harmful climate. Opinions on the climate and on whether or not the “white man” could successfully acclimatise in the Congo were not only influenced by the actual situation on the ground, but to a large extent also by whether one regarded the Congo suitable for successful exploitation by the Belgians. In addition to providing a general analysis of the debates and their connection to international developments in various fields, including colonial hygiene, the authors of this article also highlight the discourse of opponents in a number of specific discussions.