The present invention relates to an inserter for an intrauterine system, comprising a handle (3) having a longitudinal opening (8) at its first end, said opening (8) having a longitudinal axis parallel to the longitudinal axis of the inserter, a first end (8 a) and a second end (8 b), a movable slider (5) arranged in said longitudinal opening (8) and having a first end (5 a) and a second end (5 b), a plunger (2) attached to the handle (3) and having a longitudinal axis, and an insertion tube (6) having a first end, a second end and a longitudinal axis essentially parallel to the longitudinal axis of the plunger (2), the insertion tube (6) being, along said longitudinal axis, movably arranged around the plunger (2). The invention is characterised in that it further comprises a flange (4) arranged on the insertion tube (6) at its first end, and means for locking the slider (5) into a position showing the correct insertion depth for the intrauterine system, said means being adjustable with respect to the opening (8) of the handle.