The paper presents a methodology of the analysis of wrinkling in composite sandwich panels subjected to an elevated temperature and/or heat flux on one surface and compression. The solution includes a formulation of the thermal problem specifying a distribution of temperature throughout the thickness of the panel, the analysis of the effect of pre-wrinkling deformations on the wrinkling phenomenon, and the solution of the wrinkling problem, accounting for the effect of temperature on the properties of the facing and core. Numerical examples illustrate that temperature can be assumed constant throughout each facing, while the major temperature change occurs in the core. Wrinkling stresses should be determined, accounting for the effect of temperature on the properties of constituent materials. The failure to account for a degradation of the stiffness of the facing and core can lead to a dangerous overestimate of wrinkling stresses. As follows from numerical examples wrinkling may become a dominant mode of failure at high temperature.