An at least partially implantable hearing aid, having: a microphone arrangement (74) for capturing audio signals from ambient sound； an audio signal processing unit (66) for processing the audio signals captured by the microphone arrangement； an implantable actuator unit (54) for stimulating the patient's hearing according to the processed audio signals； a tube (24) for being implanted into the patient's temporal bone (26), the tube having an engagement structure (46) at the outer surface for engagement into a fixation structure (44) milled into the patient's temporal bone, wherein the tube comprises means (36) for receiving the actuator unit in an implanted condition of the tube from the proximal end of the tube and means for fixing the actuator unit in a final position relative to the tube, in which final position the actuator unit extends beyond the distal end of the tube.
