Potamopyrgus antipodarum is a New Zealand freshwater snail that is commonly infected by a coevolving and sterilizing trematode parasite, Microphallus sp. We generated RNA-Seq data for three biological replicates each of Microphallus-infected vs. uninfected P. antipodarum from each of three New Zealand lake populations (Alexandrina, Kaniere, Selfe). Each biological replicate contains 7 individuals, for a total of 18 samples (9 infected, 9 uninfected) representing 126 individuals. We used these data to evaluate patterns of gene expression and relative levels to genetic differentiation (Fst) between infected and uninfected snails within and among lakes.