Background Disseminated mycoses other than aspergillosis are infrequently reported in dogs. Case report A 4‐year‐old female Labrador retriever was evaluated because of hyperthermia, cough and intermittent lameness. Computed tomography showed a soft tissue mass in the cranioventral mediastinum, severe left and central tracheobronchial lymphadenopathy, and moderate bilateral pleural effusion. Magnetic resonance imaging identified an irregular intra‐axial well‐defined contrast enhancing mass extending from the right frontal lobe to the right thalamus. Fungal culture yielded growth of Chaetomium globosum. Conclusion In this case, the authors report a systemic mycosis in a Labrador retriever caused by C. globosum. To the best of authors' knowledge, this is the first report of systemic disease by this species in veterinary medicine.