A height adjustable footrest comprising: a treadboard part; a support structure comprising first and second leg structures (4, 5), each comprising at least one leg, the leg structures (4, 5) being hinged to the treadboard part about mutually parallel and spaced apart hinge axes (16, 17), wherein the leg structures (4, 5) cross each other in a position spaced from said hinge axes (16, 17) and are at least hinged to each other about a further hinge axis at said crossing and parallel to said hinge axes (16, 17) or to a base part about base hinge axes (20, 21) parallel to said hinge axes (16, 17) and mutually spaced apart; and an adjustment structure coupled to and extending between end portions of the leg structures (4, 5) at a treadboard side or at a base side of the leg structures (4, 5) for adjusting the spacing between the hinge axes (16, 17) at the treadboard side of the leg structures (4, 5), the adjustment structure comprising a first adjustment member coupled to one of said end portions and having a toothed rack (25, 26) oriented in a longitudinal direction and a second adjustment member coupled to the other one of the end portions and comprising a catch displaceable along the rack (25, 26) and arranged for engagement with the rack (25, 26) in selectable positions along the rack (25, 26), wherein at least the catch or the rack (25, 26) is displaceable in engagement directions transverse to said longitudinal direction between a protruded position in which the catch and the rack (25, 26) are mutually engaged and a retracted position in which the catch and the rack (25, 26) are mutually released; wherein the teeth of the rack (25, 26) each project from a base to a top in a tooth height direction transverse to said engagement directions to a counter surface (26, 25) facing said rack (25, 26) and wherein, in the protruded position in which the catch and the rack (25, 26) are mutually engaged, the catch projects into a space between the rack (25, 26) and the counter surface (26, 25) and contacts the counter surface (26, 25). a treadboard part; a support structure comprising first and second leg structures (4, 5), each comprising at least one leg, the leg structures (4, 5) being hinged to the treadboard part about mutually parallel and spaced apart hinge axes (16, 17), wherein the leg structures (4, 5) cross each other in a position spaced from said hinge axes (16, 17) and are at least hinged to each other about a further hinge axis at said crossing and parallel to said hinge axes (16, 17) or to a base part about base hinge axes (20, 21) parallel to said hinge axes (16, 17) and mutually spaced apart; and an adjustment structure coupled to and extending between end portions of the leg structures (4, 5) at a treadboard side or at a base side of the leg structures (4, 5) for adjusting the spacing between the hinge axes (16, 17) at the treadboard side of the leg structures (4, 5), the adjustment structure comprising a first adjustment member coupled to one of said end portions and having a toothed rack (25, 26) oriented in a longitudinal direction and a second adjustment member coupled to the other one of the end portions and comprising a catch displaceable along the rack (25, 26) and arranged for engagement with the rack (25, 26) in selectable positions along the rack (25, 26), wherein at least the catch or the rack (25, 26) is displaceable in engagement directions transverse to said longitudinal direction between a protruded position in which the catch and the rack (25, 26) are mutually engaged and a retracted position in which the catch and the rack (25, 26) are mutually released; wherein the teeth of the rack (25, 26) each project from a base to a top in a tooth height direction transverse to said engagement directions to a counter surface (26, 25) facing said rack (25, 26) and wherein, in the protruded position in which the catch and the rack (25, 26) are mutually engaged, the catch projects into a space between the rack (25, 26) and the counter surface (26, 25) and contacts the counter surface (26, 25).