Few studies have systematically investigated the overwintering ecology of anurans. We used large-scale field enclosures to measure the winter densities of Wood Frogs (Rana sylvatica) in an upland deciduous forest adjacent to two breeding pools in eastern Massachusetts. Pitfall traps associated with one of our enclosure arrays were operated continuously from March to December 2000. Wood Frog densities ranged from 0–6.3 Wood Frogs/100 m² (x̄ = 1.4, SD = 1.6, N = 17 enclosures) and declined as distance to the nearest breeding pond increased. The sex ratio of Wood Frogs wintering close (< 65 m) to the pond was more highly skewed toward males than the sex ratio of Wood Frogs wintering further from the pond (8:1 vs. 1.6:1). Adult Wood Frogs apparently only occupied this upland forest habitat during late fall and winter and did not use it during the summer active period. These results suggest that few wintering females may be protected within narrow regulatory buffers adjacent to breeding ponds and that the effects of habitat destruction on Wood Frog mortality may vary dramatically by season.