The grey-sided vole (Clethrionomys rufocanus) is distributed over the entire island of Hokkaido, Japan, across which it exhibits multindash;annual density cycles in only parts of the island (the northndash;eastern part); in the remaining part of the island, only seasonal density changes occur. Using annual sampling of 189 greyndash;sided vole populations, we deduced the geographical structure in their secondndash;order density dependence. Building upon our earlier suggestion, we deduce the seasonal densityndash;dependent structure for these populations. Strong direct and delayed density dependence is found to occur during winter, whereas no density dependence is seen during the summer period. The direct density dependence during winter may be seen as a result of food being limited during that season: the delayed density dependence during the winter is consistent with volendash;specialized predators (e.g. the least weasel) responding to vole densities so as to have a negative effect on the net growth rate of voles in the following year. We conclude that the observed geographical structure of the population dynamics may be properly seen as a result of the length of the summer in interaction with the differential seasonal densityndash;dependent structure. Altogether, this indicates that the geographical pattern in multindash;annual density dynamics in the greyndash;sided vole may be a result of seasonal forcing.