A hydrotherapy mattress assembly (1) which includes a core (11), a base (2) for receiving the core (11), and a top cover (4) overlying the core (11). The top cover (4) provides a patient support surface and includes a drain trough (37). The drain trough (37) is coupled to a drain (38) which extends through the core (11) and the base (2), so that liquids can be drained from the patient support surface.