A patient support apparatus comprises a base and a support frame. The patient support apparatus also comprises a lift assembly that operates to lift and lower the support frame relative to the base. The lift assembly comprises lift members that extend and collapse to lift and lower the support frame. Guides operate to guide movement of the lift members during operation. In some cases guided bodies coupled to the lift members move passively in the guides. In other embodiments, driven members coupled to the lift members move actively in the guides to cause lifting and lowering of the support frame.