Abstract: A folding truck box is designed to fit in the bed of a truck adjacent a tailgate. The truck box has a top and vertical sidewalls. The sidewalls have a height defined by a first distance between a bottom edge that rests on the bed floor and a top edge. The top overlays the sidewalls and has a second distance between a bedrail contacting surface and the surface that contacts the sidewalls. The first and second distances are greater than the distance between the bed floor and the underside of the bedrails. The top fits between the truck bedrails and the sidewalls with biased upward force on the bedrails. The truck box contains resilient retainer straps that are closed between the truck bed floor and tailgate. A locking leg in the top extends into a locking aperture in one of the sidewalls to prevent the top from being removed.