The Lascaux Cave was discovered in 1940, and by 1960 it had received up to 1800 daily visitors. In 1963, the cave was closed and in 2001 it was invaded by a Fusarium solani species complex which was treated for four years with benzalkonium chloride. However, Lascaux Cave bacteria have only been poorly investigated. Here we show that the cave is now a reservoir of potential pathogenic bacteria and protozoa which can be found in outbreaks linked to air-conditioning systems and cooling towers in community hospitals and public buildings.