The inflatable splint is formed of an inner shell of thin, semi-rigid material and at least one pneumatically inflated ply surrounding the inner shell. A second pneumatically inflated ply may be placed around the first pneumatically inflated layer. The inner shell may be lined with a soft fabric material, or a soft fabric sock or sleeve may be applied over the injured limb for comfort. The innermost semi-rigid ply of the splint may be formed in two halves that attach removably to one another to allow the assembly to be removed from the wearer from time to time for hygiene, therapy, and/or other reasons as required. The pneumatically inflatable outer plies are each formed as a single wrap. An inflation device may be provided with the assembly, for the convenience of the wearer to adjust the inflation pressure of the outer pneumatic ply or plies.