The invention relates to a length-adjustable connecting rod (1) for a reciprocating-piston machine, in particular for an internal combustion engine, comprising at least one first rod part (6) having a small connecting rod eye (2) and a second rod part (9) having a large connecting rod eye (4), which two rod parts can be moved in relation to each other and/or in each other in a telescopic manner, wherein the second rod part forms a guiding cylinder (8) and the first rod part forms a piston element (7) that can be longitudinally displaced in the guiding cylinder, wherein a first high-pressure chamber (10) is spanned between the second rod part and the piston element on the side of the piston element facing the large connecting rod eye, into which first high-pressure chamber at least one first oil channel (20) leads, in which in particular a first check valve (21) opening in the direction of the first high-pressure chamber is arranged, wherein at least a first return channel (22) extends from the first high-pressure chamber, an outflow cross-section of which return channel can be closed by a control valve (13) in a first position and can be opened by the control valve in a second position, wherein the control valve preferably has a control piston (15) that can be axially displaced in an accommodating bore (14) of the second rod part of the connecting rod, which control piston in particular can be moved into the first position by means of a return spring (16) and can be moved into the second position against the force of the return spring by means of an actuating force. In order to be able to change the compression ratio as simply as possible, the piston element according to the invention is designed as a piston that is operative at both ends.