The present invention relates to an adjustable camshaft (1), wherein inner and outer shafts (4, 2) connected securely with cams (5, 6) can be rotated relative to each other. In order to obtain this relative movement, at least one hydraulic adjusting device (3) is provided at one end of the camshaft (1), wherein a rotor (2) is rotatable in relation to a stator (19), and the rotor (20) and the stator (19) are each connected securely with one of the two shafts (2, 4). It is essential to the invention that the camshaft (1) is part of a prefabricated camshaft assembly, comprising at least the following components oriented relative to each other: camshaft (1) comprising inner shaft (4), outer shaft (2), cams (5, 6) and adjusting device (3) and a chain wheel (10).