A patient positioning system for use with a patient on a bed includes an inflatable patient support device, and optionally, other components such as one or more wedges and/or an absorbent pad. The device includes top and bottom sheets, where the top sheet is connected to the bottom sheet to define a cavity, such that the top and bottom sheets form top and bottom walls of the cavity in use. The device further has passages extending from the cavity to an exterior of the device, through the bottom sheet, and gussets connected to the top and bottom sheets and extending across the cavity. The passages permit air to pass from the cavity to the exterior of the device and to flow between the bottom surface of the device and the surface supporting the device. Selective glide assemblies may be used to resist sliding of these components in certain directions.