Although endemic throughout much of the world, autochthonous visceral leishmaniasis has been reported on only 3 previous occasions in North America. After diagnosis of visceral leishmaniasis in 4 foxhounds from a kennel in Dutchess County, New York (index kennel), serum and ethylenediamine-tetraacetic acid (EDTA)-anticoagulated blood were collected from the remaining 108 American or cross-bred foxhounds in the index kennel and from 30 Beagles and Basset Hounds that were periodically housed in the index kennel. Samples were analyzed for antibodies to or DNA of tickborne disease pathogens and Leishmania spp. Most dogs had antibodies to Rickettsia spp., Ehrlichia spp., Babesia spp., or some combination of these pathogens but not to Bartonella vinsonii (berkhoffi). However, DNA of rickettsial, ehrlichial, or babesial agents was detected in only 9 dogs. Visceral leishmaniasis was diagnosed in 46 of 112 (41%) foxhounds from the index kennel but was not diagnosed in any of the Beagles and Basset Hounds. A positive Leishmania status was defined by 1 or more of the following criteria: a Leishmania antibody titer ≥1:64, positive Leishmania polymerase chain reaction (PCR), positive Leishmania culture, or identification of Leishmania amastigotes by cytology or histopathology. The species and zymodeme of Leishmania that infected the foxhounds was determined to be Leishmania infantum MON-1 by isoenzyme electrophoresis. Foxhounds that were >18 months of age or that had traveled to the southeastern United States were more likely to be diagnosed with visceral leishmaniasis. Transmission of Leishmania spp. in kennel outbreaks may involve exposure to an insect vector, direct transmission, or vertical transmission.