The New World subfamily Hydrodytinae Miller is revised. Two genera are recognized, Hydrodytes Miller and Microhydrodytes gen. n. Hydrodytes contains three known species, H. opalinus (Zimmermann), H. dodgei (Young) and H. inaciculatus (Guignot). Microhydrodytes contains a single known species, M. elachistus sp. n. Keys are provided to the genera and species in the subfamily. Important morphological features are illustrated for diagnosing the species and a phylogenetic hypothesis is proposed for all species.