Device for measuring the axial position of a piston rod (18) relative to the cylinder housing (10) of a cylinder-piston unit that is actuated by fluid pressure, with structures having elevations or indentations formed in the jacket surface of the piston (18), which elevations or indentations form an axially extending material measure; and with a sensor device (28), which is positioned on the cylinder housing and which scans the structure with sensors that are positioned in the axial direction for the purpose of contact-free positional sensing; and with an abrasion-proof cover by means of which the structure is guided within the cylinder housing (10), where the structures are annular structures (22, 24) that concentrically surround the piston rod (18), and where the cover is a tube (26) that is coaxially slid onto the piston rod (18), and where the annular structures (22, 24) form an absolutely coded material measure.