In the course of constructing an ultrahigh vacuum apparatus employed in molecular beam scattering from crystal surfaces, we have designed, tested, and now continuously employ a simple diffusion pump cryobaffle that is mechanically refrigerated to approximately -50 degrees C. Modifications were made to a commercial water baffle for this purpose. After baking the chamber at 140-150 degrees C for three or four days, we routinely achieve a base pressure of 1-2X10(-10) Torr. Relative to a conventional liquid nitrogen trap, the cost and maintenance of the cryobaffle are minimal. The surprising feature of the baffle is its usefulness in helping generate such a high vacuum, despite the relatively high temperature of -50 degrees C. As might be expected, the baffle operates by eliminating backstreaming of the diffusion and mechanical pump fluids. However, water vapor is not cryopumped; rather, it passes through the baffle and is removed by the diffusion pump.