The structure of the zooplankton (rotifers + crustaceans) community of Adirondack lakes was evaluated relative to generalizations derived from the literature on the impacts of acidification. The generalization that the number of zooplankton species is reduced in acid lakes was strongly supported by the results of Adirondack studies. Acidity status appeared to be the most important factor determining zooplankton species richness in Adirondack lakes. Generalizations regarding community composition were not strongly supported. Although the relative biomass of daphnids and cyclopoid copepods tended to be reduced in acidic lakes they were also frequent dominants of the communities of acidic lakes. Only two of the “generalist” species of the Adirondack region, Diaptomus minutus and Keratella taurocephala, increased in relative importance in acidic lakes. Acidification had a significant effect on zooplankton biomass.