Blastomycosis was diagnosed in 6 dogs living in New York state. To our knowledge, blastomycosis has not been previously reported in dogs in this area, and maps that indicate the prevalence of blastomycosis in North America often partially or completely exclude the state of New York. Environmental characteristics implicated in previous blastomycosis outbreaks in people can be found in New York state, and this may explain how these dogs became infected. Blastomycosis develops in people as well as in dogs, and an understanding of the ecologic and clinical features of blastomycosis can help veterinarians counsel their clients in matters of public health.