Natural convection flows are studied numerically for porous media and homogeneous fluids inside a rectangular cavity with inclination. These thermal fluid flows are considered under the respective two-dimensional unsteady Boussinesq approximation in stream function and vorticity variables. The study depends on the Rayleigh number, angle of inclination, and the aspect ratio of the cavity. At the validation stage our results are in good agreement with those reported by other authors. Results suppose to be new are presented either for angles of inclination not reported before or for high Rayleigh numbers with large aspect ratios. In rectangular porous cavities with Rayleigh number >= 10(2) multiple cells appear for some angles. In homogeneous fluids, for Rayleigh numbers of the order of 10(5)-10(6) in large enough vertical cavities at most secondary cells appear for some angles and the flow becomes more complex and looks like to be oscillatory. (c) 2006 Elsevier Ltd. All rights reserved.