A finger splint assembly includes a generally cylindrical sleeve having a wall of flexible but inextensible material and opposite proximal and distal ends which are open. The remaining component of the assembly is a shim having opposite relatively thick and relatively thin ends and a flat top surface extending between those ends. The shim is longer than the sleeve such that when the shim is inserted, thin end first, into the distal end of the sleeve with its top surface aligned with an internal chord of the sleeve and with one of the thick and thin ends lying within the sleeve, the other of the thick and thin ends projects from the corresponding end of the sleeve. A method of using the assembly to treat Mallet Finger is also disclosed.