An one-year-old male roe deer (Capreolus capreolus) with abnormal behaviour was shot in order to exclude rabies virus infection. The 12.8 kg weighing animal was emaciated and revealed an asymmetric head with protruding left eye and expositional keratitis. There was a grey whitish soft mass within the caudal nasal cavity, which had infiltrated the frontal cerebrum through the cribriform plate and the retrobulbar tissue through the orbita. Histologically, the mass consisted of a chronic granulomatous inflammation with plentiful fungal hyphae. Fungal culture revealed mold fungi of the zygomycotic genus Rhizomucor, which were differentiated as Rhizopus microsporus by MALDI-TOF mass spectrometry and DNA-sequencing. Rhinoorbitocerebral zygomycosis has to be considered as a differential diagnosis for nasal and orbital tumour-like lesions and as a cause of abnormal behaviour of roe deer.