A two-year-old intact female collie presented with a tentative diagnosis of systemic blastomycosis based on compatible clinical signs and history and a positive urine Blastomyces antigen enzyme immunoassay. The dog was subsequently correctly diagnosed with protothecosis based on ocular and paw pad histopathology and in vitro culture of Prototheca wickerhamii from paw pad tissue. Histopathology revealed organisms in deep tissue samples as well as in the epidermis and superficial keratin layers of the paw pad. Serum (1→3)-β-d-glucan testing was negative. The dog was treated with terbinafine based on in vitro susceptibility results. There are no previous reports of terbinafine use for the treatment of canine protothecosis. Neurological and gastrointestinal symptoms remained stable with terbinafine. While there was an overall improvement in cutaneous lesions and attitude over the course of eight weeks on treatment, the animal did not survive despite therapy.