Whole-body positron emission tomography (PET) imaging with fluorine-18 fluorodeoxyglucose (F-18 FDG) was performed in a dog with blastomycosis. Prior to PET scanning, blastomycotic lesions had been identified in both eyes, lungs, and tracheobronchial lymph nodes. Increased F-18 FDG uptake was present in these sites in addition to multiple organs without previous clinical evidence of disease. All sites of F-18 FDG uptake were confirmed histologically to be blastomycotic granulomas. F-18 FDG-PET scanning may be useful for defining the extent of fungal disease and detecting persistent foci of infection.