A bunk bed structure having a vertically movable upper bunk provides a main frame having two spaced corner posts at each end interconnected by end cross pieces in their upper extensions, with a side support interconnecting the upper portions of each end post on one side of the main frame. A lower bunk frame having a depending medial portion to support a bed board and bedding is carried by four tubular corner collars on the lower portions of each of the corner posts. A similar upper bunk frame is slidably carried by four tubular corner collars on the corner posts for vertical motion above the lower bunk frame. Each upper bunk corner collar has associated fastening pins that releasably fasten and positionally maintain the collar on its associated corner post. The bunk structure frames are formed of tubular pipe elements interconnected by fixtures commonly used to join such elements and the pipe elements, especially if formed of plastic, may carry more rigid rods or tubes in their medial channels to increase strength and rigidity.