There is currently intense research on sulfur/carbon composite materials as positive electrode for rechargeable batteries. Preparation of such composites by ball milling or (melt/solution) impregnation are popular approaches to obtain intimate contact between both compounds with the hope to improve battery performance. Here, we report that sulfur shows an unexpected “spillover” effect in contact with porous carbons under ambient conditions. When gently mixing sulfur and porous carbon (e.g. 1:1 mass ratio), complete surface coverage takes place within just a few days along with the loss of sulfurs bulk properties (crystallinity, melting point, Raman molecular vibrations vibrational structure). Sulfur spillover also occurs under presence of a liquid phase. Consequences of this phenomenon are discussed using a sodium-sulfur cell with solid electrolyte membrane. Overall, sulfur spillover on carbon is a so far overlooked phenomenon that we expect to have great relevance for all types of metal-sulfur batteries with porous carbon a support.