A modular hearing aid for arrangement in a user's ear comprises a hollow plug (1) adapted to the ear canal and having a generally irregular conical shape and an exterior opening which is covered by a faceplate (2), in which a recess (8) is formed for removable arrangement of a battery (23) as well as an electronic module (4) comprising a microphone part (5), a signal processing part (6) and a sound reproducer (7). The recess (8) comprises a first region (9) for insertion of the battery (23) and a second region (10) coherent with the first region for placing of a socket part (11) of the electronic module (4), and at the edge of the recess (8) the faceplate (2) is formed with engaging means (12-16) for the socket part (11), whereas further parts of the electronic module (4) are placed below the faceplate (2). The recess (8) is formed such that at removal of the battery (23) the first and second regions (9, 10) together allow passage also of said further parts (6,7) for removal of the complete electronic module.