Abstract: An extension bed for extending the cargo space of a truck of the type having a truck bed including a floor, side walls, and a tailgate is readily installed in any standard-sized pickup truck and is easily slidable from its retracted, storage position within the truck bed to an extended position supported by the open tailgate of the truck. The truck cargo space extension bed includes an extension floor, an extension tailgate, and opposing upright extension side walls having a substantially t-shaped channel extending the length of the side walls and corresponding t-shaped pins mounted to the pickup truck for slidably connecting the extension bed to the pickup truck side walls. The t-shaped channels include a stop mechanism for preventing the extension bed from becoming accidently disengaged from the pickup truck and a latch on the extension bed for selectively locking the extension bed in the extended position.