Adjustment mechanism , in particular for a headrest for a seat, which has a scissor lever comprising at least one first lever arm and at least one second lever arm , which can be pivoted in relation to one another about a common main pivot axis (S) at a common point of intersection (P), characterized in that - a compensating lever arm is arranged at precisely one lever-arm end of each lever arm so as to be pivotable about a compensating pivot axis (AS1, AS2), which runs parallel to the main pivot axis (S), wherein - a free end of the respective compensating lever arm comprises a fastening structure for fastening the compensating lever arm on a body, and - a lever-arm end located opposite the compensating lever arm of the respective lever arm comprises a fastening structure for fastening the lever arm on a body, wherein the pivotable arrangement of the respective compensating lever arm on the associated lever arm is implemented by a pivot bearing , wherein - the pivot bearing comprises a bearing shell (18.1), which is arranged on the compensating lever arm or on the lever arm and has an opening (O) penetrating the bearing shell (18.1), and comprises a bearing body (18.2), which is arranged on the lever arm or on the compensating lever arm and corresponds with the bearing shell (18.1), - wherein a distance between bearing surfaces (L1, L2) of the bearing body (18.2), these bearing surfaces corresponding with the bearing shell (18.1), is smaller than an internal diameter of the bearing shell (18.1) and larger than a width (B2) of the opening (O), and - wherein a width (B1) of the bearing body (18.2), this width extending at least substantially perpendicularly to the aforementioned distance, is smaller than the width (B2) of the opening (O). - a compensating lever arm is arranged at precisely one lever-arm end of each lever arm so as to be pivotable about a compensating pivot axis (AS1, AS2), which runs parallel to the main pivot axis (S), wherein - a free end of the respective compensating lever arm comprises a fastening structure for fastening the compensating lever arm on a body, and - a lever-arm end located opposite the compensating lever arm of the respective lever arm comprises a fastening structure for fastening the lever arm on a body, wherein the pivotable arrangement of the respective compensating lever arm on the associated lever arm is implemented by a pivot bearing , wherein - the pivot bearing comprises a bearing shell (18.1), which is arranged on the compensating lever arm or on the lever arm and has an opening (O) penetrating the bearing shell (18.1), and comprises a bearing body (18.2), which is arranged on the lever arm or on the compensating lever arm and corresponds with the bearing shell (18.1), - wherein a distance between bearing surfaces (L1, L2) of the bearing body (18.2), these bearing surfaces corresponding with the bearing shell (18.1), is smaller than an internal diameter of the bearing shell (18.1) and larger than a width (B2) of the opening (O), and - wherein a width (B1) of the bearing body (18.2), this width extending at least substantially perpendicularly to the aforementioned distance, is smaller than the width (B2) of the opening (O). <EOS>