A convective thermal blanket is provided which warms or cools a patient's head and body areas by convection. The blanket includes a covering which has top and bottom layers of material, the covering being sealed along its periphery so as to form a plenum chamber. The head end of the covering has a recess for receiving a patient's head. The recess forms the head end of the covering into a pair of flaps, each flap being adapted to extend along a respective side of the patient's head and the covering below the recess being adapted to cover the patient's chest or body area. The recess also forms the plenum chamber into a main plenum chamber for the chest area and a pair of secondary plenum chambers, each secondary plenum chamber being in a respective flap for the head area. The covering has an inlet opening for receiving a gaseous medium for inflating the main plenum chamber and the secondary plenum chambers. The bottom layer of the covering has a plurality of apertures, which open into the main plenum chamber and the secondary plenum chambers, for discharging the gaseous medium over the patient's chest and head areas when the plenum chambers are inflated.