An instrument system is provided. The instrument system has an endoscopic instrument with a work head that is mounted on one end of a flexible support arm and can be inserted into a patient. The instrument system has a trocar that can be placed in the body surface of the patient and has a main body which can be fixed in position relative to the patient and which has a through-opening for the instrument, a guide body which, when the instrument is inserted, encloses and guides a longitudinal portion of the support arm with a guide channel in such a way that a spatial guiding direction of the support arm is defined at least thereon, with an adjustment element acting on the guide body and allowing a specific change of a relative position of the guiding direction with respect to the main body.