The surface roughness of painted and unpainted panels was measured. Great differences were observed on panels subjected to different methods of accelerated aging. The increase in some accelerated aging tests was greater than the corresponding decrease in strength, and depending mainly on how water penetrated into the panels during aging. Among various types of unpainted panels there were significant differences in surface stability on accelerated aging. Fiber building boards exhibited much larger surface stability than particle boards, independent of the type of resin used. Panels of solid wood showed only minor surface changes, whereas in plywood the initial microcracks deepened markedly. Natural weathering during the four year exposure at an angle of 45° facing south seemed to degrade the surface less than the accelerated methods. However, other defects were observed after natural weathering. The methods for accelerated aging are more suitable for production control of specific panels than for evaluating the surface properties of wood-based panels. -- AATA