We report on phenotypic plasticity in the frequency of reproduction in a viviparous, alpine scincid lizard (Niveoscincus microlepidotus) from Tasmania, Australia. After having monitored individually marked females for five years in the wild, we conclude that females never reproduce two years in succession. Instead, female reproduction is biennial to triennial (for those that survive their first reproduction). However, when offered prolonged benign conditions indoors, females may give birth in summer, that is, showing annual reproduction. We have demonstrated elsewhere that full-term females refuse to give birth in autumn when temporarily offered 'summer temperatures.' Thus, females seem only to go through with parturition within a 'temporal window' in summer but refuse parturition closer to hibernation, through which the full-term young are carried by the female.