EN
The variability of body and skull dimensions was examined in a population of the root vole, Microtus oeconomus (Pallas, 1776) from high mountain habitats, Hardangervidda, southern Norway. Morphometric analysis was made on 530 of 915 specimens obtained over an 8 year trapping period (1970 - 1978), taking into account sex, age class, season and population cycle. Sexual dimorphism was distinct in the oldest age group, in which males were significantly larger than females. The specimens from the peak phase were larger in body and skull dimensions (Chitty Effect). The influence of age structure on fluctuations in body size during the microtine cycles is discussed.