Abstract: A split jamb prehung door assembly wherein a door is connected to a side jamb part by a split hinge assembly in which one plate has multiplanar parts, one part mounted to the side jamb and another part extending normally to the side jamb part against a door casing. Sizing clips are further mounted on the spaced side jambs, and such clips have rearwardly extending arms which are deformable so that they can be moved and fastened to the adjoining wall studs of a doorway opening, such sizing clips further mounting the door casing to the jambs so that preformed apertures in the normally extending plate and clip parts are registered with preformed openings in the casing to allow fasteners to be passed through the registered openings and into the adjoining wall studs. A mating jamb and casing member is then moved into the doorway to interlock the mounted door jamb sides and connect a top jamb part.