An adjustable camshaft has at least one adjusting element of an adjusting system fixedly connected to inner and outer shafts that is at least partially in tight contact at the end with a connection surface which is formed by a mounting ring of the outer shaft with respect to the two shafts including the mounting ring. The connection surface is crossed by axial passages between hydraulic chambers of the adjusting system and by hydraulic liquid supply ducts which extend through the shafts, between the shafts and/or through annular gaps formed between the outer shaft and the mounting ring, from the connection surface to filling zones which are located in the peripheral surface of the mounting ring and open into circumferential ring-shaped channels associated each with a filling zone of a supply duct.