The freshwater fish leeches of North America are poorly studied taxonomically, and criteria for genus assignment, especially for the morphologically similar genera Piscicola and Cystobranchus, are based on the better-studied European fauna. In this study, we redescribe the internal anatomy of Cystobranchus virginicus and Piscicola salmositica from North America on the basis of serial sections. Cords of conducting tissue connecting the bursa to the ovisacs and accessory gland cells on the atrial cornu are present in both C. virginicus and P. salmositica. Presence or absence of accessory gland cells should not be used as a character to distinguish Piscicola from Cystobranchus. Piscicola is characterized by the presence of an external copulatory area and cords of conducting tissue arising from a ventral mass of vector tissue. Cystobranchus is characterized by the absence of an external copulatory area and the presence of cords of conducting tissue arising from the posterior portion of the bursa. These observations confirm the previous placement of Cystobranchus salmositicus.