A computer-aided 3-D reconstruction and measurement method was used to assess postnatal volume and height changes in the tympanic cavity. Materials used were 14 normal human temporal bones obtained from 6 infants (under 1 year of age) and 8 adults (over 18 years of age). After defining the boundaries of the tympanic cavity, its total volume and height and the volume and height of the epitympanum, mesotympanum and hypotympanum were measured. The relationship between the volume of the tympanic cavity and age, and the correlation between the volume of the tympanic cavity and the grade of pneumatization of the air cells were also studied. The average volume of the tympanic cavity in adults (640.1+/-69.1 mm3, n = 8) was about 1.5 times larger than the volume of the infant cavity (451.7+/-68.2 mm3, n = 6). The hypotympanum increased most postnatally and the mesotympanum least. The volume of the tympanic cavity increased in proportion to increasing pneumatization in bone surrounding the cavity. The postnatal increase in the height of the tympanic cavity appears to be the major contributor to the increase in volume of the cavity. Postnatal changes in the tympanic cavity have clinical implications.