This paper illustrates a study on the punching shear strength of reinforced concrete slabs in fire conditions. To this end, a set of experimental data on the punching strength of heated slab specimens was interpreted by adapting the well-known Critical Shear Crack Theory to include the effects of high temperature and fire. The comparison between experimental and numerical results is rather good, considering the several uncertainties affecting the problem under consideration. It turns out that the proposed approach is a reliable tool to evaluate the punching strength of thermally-damaged slabs, and this is a good premise for a more in-depth study of the behaviour of punching-sensitive flat slabs in fire conditions.