Garlic mustard (Alliaria petiolata) is a non-native invasive herb that has the potential to alter the understory plant community. We investigated the reproductive output of garlic mustard as a function of plant size and conspecific and heterospecific density in a central Ohio population. In general, taller plants produced more reproductive units (seeds, siliques). Density of conspecifics and heterospecifics had no effect on plant height or reproductive output. Reproductive output in our population of garlic mustard is lower and mean seed size is larger than most other populations for which data have been published, possibly because of the dry upland habitat of our population.