The effect that three different radiopacifying agents, two of them inorganic (BaSO4, ZrO2) and one organic (an iodine containing monomer, IHQM) have on the static and dynamic mechanical properties of acrylic bone cements was studied. Compressive and tensile strength, fracture toughness and fatigue crack propagation were evaluated. The effect of the inorganic fillers depends on their size and morphology. In relation to the radiolucent cement, the addition of zirconium dioxide improved significantly the tensile strength, the fracture toughness and the fatigue crack propagation resistance. In contrast, the addition of barium sulphate produced a decrease of the tensile strength, but did not affect the fracture toughness and improved the crack propagation resistance. When the iodine containing monomer was used, although the tensile strength and the fracture toughness increased, the fatigue crack propagation resistance remained as low as it was for the radiolucent cement.