We have investigated the dependence of several anatomical parameters of the guinea‐pig middle ear on body weight, and thus on age. In particular, the volumes of the tympanic and epitympanic cavities are found to increase with age, with the tympanic cavity growing somewhat more slowly. The mass of the incus appears to be independent of body weight. These results are important for establishing the values of parameters used in mathematical models of the middle ear. They are also relevant to theoretical considerations of the significance of middle‐ear resonances.