The biology of the gypsy moth, Lymantria dispar (Lepidoptera:Lymantriidae), in the northeastern US is well described, yet we know little about its population dynamics in new habitats into which it is currently spreading westward. Likewise we know little about the major factors regulating its abundance at low densities in general. We examined the effects of habitat structure on the population dynamics and natural enemy associations of recently established gypsy moth populations in northeastern Wisconsin. Forty-five forested sites having a range of basal areas from 80-155 sq.ft./acre were established in northern hardwood forests dominated by northern red oak, Quercus rubra. Population sampling of all life stages was conducted for two years, along with direct experiments surveying for natural enemies. Under these suboutbreak conditions (50-20,400 masses/hectare), no noticeable defoliation occurred. Predation appeared more important than parasitism, and the fungal pathogen Entomophaga maimaiga and nuclear polyhedrosis virus were present at all sites sampled. However, mating success did not appear to be a limiting factor, even at the most sparsely populated sites. Impacts of the various natural enemies on gypsy moth survival varied with habitat structure. These results may partially explain why gypsy moth populations appear to spread more rapidly along its western leading edge. In addition, they may help guide the implementation of silvicultural strategies to managing this invasive defoliator.