The problem of laminar free convection in a trapezoidal enclosure, filled with a fluid-saturated porous medium and with internal heat generation has been investigated using a penalty finite element analysis. The enclosure bottom wall is heated at a constant temperature and the top wall is subjected to a constant cold temperature whereas the left inclined wall is considered to be non-isothermal and the right inclined wall is isothermally cooled. The effects of the porosity of the medium and heat generation on the isotherms and streamlines are investigated. The rate of heat transfer from the walls of the cavity is examined as well. The Prandtl number of the fluid is chosen to be 0.7 (air) whereas the value of the Rayleigh number is selected to be 105.