A combination unit for attachment to a hearing aid includes an adapter and an accessory, having mating guideways, respective assembly pressure faces (14,29) adjacent the guideways and respective disassembly pressure faces (13, 30), also adjacent on the guideways. The adapter (2) includes a shoe, i.e. a sleeve-like structure, adapted to partially enclose the lower portion of the hearing aid. The accessory (3) may include a miniature FM receiver. The receiver housing (22) exterior is tailored to match the adapter exterior in order that the respective walls are flush when the parts are assembled. The combination unit (1) of the adapter and the accessory is easily assembled and easily disassembled, and is very compact. The invention provides a combination unit, including the shoe and the accessory, as well as a method for attaching an accessory to a hearing aid.