The in-the-ear hearing aid (10) has a collar (30) which can form a seal in the bony part (3) of the ear canal (1), which reduces the occlusion effect. The collar (30) comprises a tubular portion (31) which is engageable against the wall (9) of the ear canal, a fixing portion (32) and a curved sealing portion (33). Owing to the use of this collar (30) it is not necessary to make a mould of the bony part (3) of the ear canal. This collar enables the hearing aid to be constructed in such a manner that it can be inserted so deep into ear canal that it is substantially invisible.