Litter fall was studied on gypsy moth (Lymantria dispar (L.))-defoliated plots and undefoliated plots in a Pennsylvania oak forest. Litter, collected throughout the year, was separated by plant and insect component and analyzed for dry weight and five major nutrients. Total biomass of litter falling on the defoliated and the undefoliated areas was not significantly different. Within the undefoliated plots, 90% of the litter was deposited during the autumn, and tree leaves were the major litter component. Major litter components within the defoliated plots included insect frass, leaf fragments, and tree leaves; 56% of the litter was deposited during the growing season. The nutrient content of litter totaled 73.1 kg/ha on the undefoliated plots, and tree leaves contributed 85% of all nutrients. The nutrient content of litter on the defoliated plots amounted to 94.6 kg/ha; leaf fragments, insect frass, and tree leaves contributed 34, 25, and 29% of all nutrients. Gypsy moth defoliation caused a statistically significant increase in the quantities of N, P, and K and a significant decrease in the quantity of Ca contained in litter fall. These differences are attributed to the gypsy moth altering the composition and seasonal distribution of litter fall. The significance of this nutrient shift is viewed as a further detriment to the health and vigor of host trees. Forest Sci. 32:855-870.