Visceral leishmaniasis is an endemic protozoal disease of humans and dogs in tropical and subtropical regions in Asia, Africa, southern Europe, Central America, and South America, where sand flies (genera Phlebotomus and Lutzomyia) act as vectors. An outbreak in a New York foxhound kennel and subsequent surveillance revealed widespread Leishmania infantum infection of dogs in the United States, outside the known range of the vector sand flies. For this study, we conducted surveillance for sand flies during the summers of 2001 and 2002 at two areas: on the grounds of the New York kennel and at the Institute of Ecosystem Studies (IES) 10 km away. CO2-baited light traps were used for surveillance. Populations of Lutzomyia vexator, not previously known in New York, were widespread and locally abundant (range, 0.26-1.16 flies/trap night) at the IES site. These populations showed a bimodal, midsummer activity peak and were most abundant on steep slopes within mature mixed hardwood forests. Further research will be necessary to determine whether the New York populations of L. vexator in the vicinity of the kennel could be involved in transmission of canine leishmaniasis.