Abstract: A retractable stair system for vehicles. The apparatus includes stairs which are retractable into a frame, or extendable to provide a set of stairs with relatively uniform height therebetween. Indexing plates with locking notches and companion latches with latch tongues to fit in the notches enable adjustment of the height of a top step S1 in a set of steps in an extensible-retractable stairs assembly. Extensible legs are provided which are individually vertically adjustable to provide secure engagement with an uneven substrate such as rocky ground or a sloping surface. Foot pads are pivotally attached to the extensible legs. The combination of vertical adjustability, the selection of a desired number of stairs, and individual top stair height adjustability, make the unit adaptable for use in a variety of vehicles.