A steerable ultra-low patient bed incorporates means for maintaining verticality of the caster stem at all height positions of the bed, and means for selectively locking the caster assemblies of the bed in a desired locking position. The means for selectively locking the caster assemblies may be actuated from either end of the bed using a central actuation mechanism. The bed preferably has legs that are pivotally and translatably attached at their upper end to the bed frame, and caster support members that are longitudinally aligned with the bed pivotally attached to the lower end of each leg. Each caster support member has a single caster assembly attached thereto. The means for maintaining verticality of the caster stem incorporates a constraint means that urges the caster support member in a direction of rotation opposite that of the leg during adjustment of the height of the bed.