A toothbrush holder adapter is provided which consists of an integral, unitary component with a toothbrush receiving section and a rear section adapted to be inserted into the holes or openings in a wall-mounted toothbrush holder. The receiving section of the member comprises dual side members forming a tapered opening into which a toothbrush is inserted and retained below its brush head. The dual side members merge to form the rear section, an extension portion which is insertable into an opening in the holder. The adapter is entirely coated with rubberized or plastic-type coating to assist in gripping the surfaces of the holder and the toothbrush handle, and in maintaining the adapter securely in the holder when a toothbrush is positioned in it. In an alternate configuration the extension portion of the adapter can be secured to a suction cup, in order to allow the adapter to support a toothbrush on a substantially vertical surface, such as a mirror or tile wall.