The invention relates to a medical instrument with an elongated element and an end effector (200) arrangeable at one end of the elongated element. The end effector (200) is operable by means of a hydraulic actuating mechanism (100), and the hydraulic actuating mechanism (100) has a cylinder body (110) with at least one, preferably two, three, four or five, overflow channels (112a, 112b, 112c) for a hydraulic fluid, the overflow channels being connected via at least one bore to the interior of the cylinder body (110). A piston (140) movable along the longitudinal axis (A) of the cylinder body (110) is provided in the cylinder body (110). The piston (140) subdivides the interior of the cylinder body (110) into a first cylinder chamber and a second cylinder chamber and is connected via a piston rod (141) to the end effector (200). At least one connection (123) for introducing hydraulic fluid into the first cylinder chamber and at least one further connectinion (124a, 124b, 124c, 124d, 124e), connected to at least one first overflow channel (112a, 112b, 112c) of the cylinder body (110) are provided, and at least one passage (130) for a surgical or optical instrument, the longitudinal axis of which substantially coincides with the longitudinal axis (A) of the cylindrical body (110), is arranged in the interior (113) of the cylinder body (110).
