Abstract: An improved accordion-like folding cover for open truck beds includes a flexible waterproof canvas cover overlying a plurality of elongated metal panels hingedly joined to form a cover assembly. The cover assembly is foldably mounted between a pair of guide tracks which are attached to the upper surface of the side walls of the truck bed; the tracks being attached to the side walls by bolts which are concealed from the exterior of the closed truck bed. An improved locking mechanism comprises a handle and a pair of attached locking arms which extend perpendicularly to and selectively into engagement with the tracking components. By turning the handle, the locking arms are retracted or extended into selected ones of a plurality of slots in the side walls of the tracks for holding the cover in a plurality of positions including fully opened, partially opened, or completely closed. The handle may be locked by a key and the locking arms are concealed beneath the cover assembly for security.