Canine aspergillosis differs from its incidence in all other species. All but one of the reported cases in the dog have occurred in the nasal cavities or paranasal sinuses, whereas respiratory aspergillosis in man, cats, cattle, horses, and rabbits usually occurs in bronchopulmonary form. In man, infection of the paranasal sinuses has been reported and in horses gutteral pouch infection with Aspergillus species is not uncommon. Mycotic infection must be included in the differential diagnosis along with neoplasia, chronic bacterial sinusitis, foreign bodies and Linguatula serrata infestation of any dog presented with a chronic nasal discharge. The ubiquitous Aspergillus fumigatus is the most common fungal invader although other Aspergillus species and rarely Cryptococcus neoformans are isolated from the dog. The usual clinical picture is one of chronic rhinitis with sneezing, lethargy, and a unilateral nasal discharge as the presenting signs.