A bed assembly (10) includes a frame (22) which supports four curved mattress support panels (50-56) which are able to move with pivoting of the various parts of the frame (22). The curved panels (50-56) better conform to a patient's body shape and provide an effective lengthening of the mattress support (50-56), particularly when the back rest (30, 50) is raised to a sitting position. The support panels (50-56) are located below the pivot points of the frame (22), which further enhances the lengthening effect. The assembly also includes first and second patient retention panels (80, 82) with complementary edges (92, 94) which can slide over one another. A key pad unit (100) protrudes from the retention panel (80) at a convenient patient position and can be gripped by a patient's hand.