In odontocetes the mandibular bone serves two functions: to capture prey, and as a means of the reception and transmission of sound waves through a fat body in the mandibular canal, which opens posteriorly as the mandibular foramen. The posterior part of the lateral wall of the odontocete mandible is thin, and appears to represent a compromise between a strong mandible for prey capture and a thin vibrating plate for hearing. We studied the intraspecific variation of minimum thickness of the lateral mandibular wall along four transects (T1-T4) at the area of the mandibular foramen, in relation to the skull size and the mandibular size in different-aged bottlenose dolphins, Tursiops truncatus (18 females between 1 and 42 yr, 17 males between 1 and 32 yr). The minimum thickness was absolutely at its lowest at the most posterior transect T1, but did not vary significantly between the sexes or between the ages. The minimum thickness varied significantly at the two most anterior transects, T3 and T4, both between the sexes and among the ages. The thickness increased throughout life among males, whereas in females it first increased and then starts to decrease around the age of 20.