Wood mouse (Apodemus sylvaticus) populations are expected to show a peak in autumn in the year after a mast year of sessile oak (Quercus petraea), because stored acorns increase winter survival. In Aust-Agder, South Norway, only 16 of 34 mast years from 1939-2014 were followed by a year with a peak in the wood mouse population. For many of the remaining instances, there rather was a minor peak 2 or 3 years after the mast. In multiple logistic regression models, the probability of a wood mouse population peak after a mast year of sessile oak was positively related to a snow-corrected temperature index of the previous winter and negatively to a small rodent population index of the previous autumn. The present study thus supports the hypothesis that longer periods with snow-free ground and subzero temperatures negatively affect wood mouse winter survival. Because it may be difficult for wood mice to survive on a diet consisting of acorns alone, the negative relationship with the rodent population index of the previous year is most likely caused by an over-exploitation of necessary alternative food resources, such as other plant seeds and arthropods. Stored acorns not utilized during one winter are assumed to benefit wood mice in a succeeding winter, giving a delayed population peak relative to the mast year.