In a sheath device for inserting a catheter into a patient's body, comprising a first sheath (10, 11, 13, 21, 21′, 21″, 41, 43) having a proximal end and a distal end, wherein when used as intended the distal end of the first sheath is provided for arrangement in the patient's body and the proximal end of the first sheath is provided for arrangement outside the patient's body, and wherein the first sheath comprises a tubular section (11, 21, 21′, 21″, 41) and a sheath housing (13, 43), which is disposed at the proximal end of the section and comprises a receiving channel (46) for a catheter, according to the invention the tubular section (11, 21, 21′, 21″, 41) is detachably held in a clamping element (45, 48, 50, 62, 63, 64) of the sheath housing in a non-positive manner so as to be able to easily shorten the tubular section.