Field hatch of gypsy moth, Lymantria dispar (L.), is an important population parameter of interest to both managers and researchers. It has been problematic to quantify hatch in the field without affecting its outcome. A method for quantifying hatch after it has naturally occurred in the field is presented. This technique uses a previously developed regression model for estimating fecundity, coupled with a count of unhatched eggs, to calculate the proportion of hatch. Hatch estimates were regressed against known hatch from a laboratory population to test the performance of the method ( r 2 × 0.90, p × 0.0001). The method can be used to estimate first-instar hatch on an individual egg-mass basis or for a population.