In a sheath device for inserting a catheter into a patient's body, comprising a first sheath 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 and a sheath housing, which is disposed at the proximal end of the section and comprises a receiving channel for a catheter, according to the invention the tubular section is detachably held in a clamping element of the sheath housing in a non-positive manner so as to be able to easily shorten the tubular section.