An adjustment mechanism for a helmet. A first sliding surface is defined in a first portion of the helmet and includes an opening. A second sliding surface is defined in a second portion of the helmet. Two spaced apart arms extend from the second sliding surface. The first and second sliding surfaces are in sliding engagement with one another with the arms sliding within the opening. A lever is pivotally connected to the first portion in proximity of the opening and pivotable between a locked position and an unlocked position. The lever has a series of regularly spaced apart parallel teeth which in the locked position protrude through the opening with at least a selected one of the teeth being engageable between the two spaced apart arms to prevent the first and second sliding surfaces from sliding relative to one another.