Mycosis of the guttural pouches is a sporadic disease characterized by diphtheroid-necrotizing inflammation, and is caused by different fungal species, mainly by Aspergillus spp., Penicillium spp. and Candida spp. Highest incidence is during summer in stable horses. Proper diagnosis often requires--besides detection by mycological techniques--histological examination of tissue obtained by bioptic endoscopy. Prognosis is hopeless in late stages of the infection because of the erosion of the carotid artery or accompanied by the fatal complications of a not reparable cranial nerve damage also in cerebral penetration. Therefore, early diagnosis is very important for the initiation of effective antimycotic therapy. The clinical features of the disease and the possibilities for diagnosis and therapy will be presented in detail.