A numerical investigation of combined radiation and natural convection in slanted cavities of angle 45° and 60°, respectively, has been performed for a temperature ratio of Th/Tc = 2, and Tc = 500°K. The finite volume method is used to solve the Navier Stokes, temperature and the Radiative Transfer equations, for constant thermo-physical properties and Ra = 105. The Boussinesq approximation is used to model the buoyancy. Cases of pure convection and of convection and radiation, in both a transparent and in a radiative participative medium, have been compared using the flow and isotherm patterns and the local convective, radiative and total Nusselt numbers. The radiative optical length of the medium shows a marked effect on the recirculation rate, temperature distribution and the overall heat transfer. The wall emissivity also shows a strong influence on the heat transfer whereas the scattering albedo does not do so. There is a decrease in the recirculation rate as well as the overall heat transfer with the increase of slant of the geometry. Additionally, a non-Boussinesq variable density formulation is also tested on the same geometry and conditions. The total average Nusselt number shows little significant difference between the results from the Boussinesq and the variable density formulations. © 2012 Elsevier Masson SAS. All rights reserved.