An adjustable mount for anchoring a safety belt on a vertical surface of a motor vehicle has a vertically elongated guide rail fixed to the surface and having an front face turned away from the surface and a rear face turned toward the surface. This rail is formed with a longitudinally extending throughgoing slot and generally along the full length of the slot with a vertical row of stops at the rear face and having upwardly and downwardly directed stop edges. A slider displaceable along the rail has a rear portion engageable forward with the rear face of the rail and having abutments engageable between the stops with the edges thereof, a front portion engageable rearward with the front face of the rail, and an intermediate connecting portion extending between and unitarily interconnecting the front and rear portions. A guide fixed to the rear portion extends forward therefrom through the slot and is formed with a forwardly open threaded bore into which a bolt is threaded. A spring braced between one of the faces and the slider urges the rear portion forward against the rear face. This rear portion is displaceable rearward on loading of the spring to a position with the abutments clear of the stops and with the slider displaceable longitudinally along the slot. A buckle traversed by the belt is mounted on the slider.