In an adjustment device for a camshaft of an internal combustion engine for varying the phase relationship of a camshaft with respect to a crankshaft as a function of the operating point of the internal combustion engine, the adjustment device comprises an epicyclic gear structure with a drive-side and an output side ring wheel, which are in meshing engagement with planet wheels, and the output-side ring wheel has a number of teeth different from that of the drive-side ring wheel so that the position of the camshaft relative to the crankshaft can be adjusted via an electric servomotor which drives a central sun wheel.