In accordance with the system of viral species, viral disorders of the oral mucosa may be classified with regard to their intensity of affection. There are but few viral infections exclusively affecting the oral mucosa like e.g. 1. Glossitis papulosa of Michelson, representing a special form of vaccinia inoculata, 2. Gingivo-stomatitis herpetica and 3. warts of the mucosa or condyloma-like papillomas of the oral mucosa including oral papillomatosis, that, itself shows morphological and clinical similarities to laryngeal papilloma. A second group of disorders mainly affecting the oral mucosa includes the "Aphthoid of Pospischill and Feyrter", Zahorsky's herpangina and other viral infections by the Coxsackie group, like vesicular stomatitis. The 3rd group represents viral infections of other organs in which affection of the oral mucosa is a prerogative, e.g. smallpox, varicella, foot-and-mouth disease and pharyngo-conjunctival fever. A 4th group includes those viral infections of the organs in which co-affection of oral mucosa occurs frequently or once in a while (at occasions). Here, we find eczema vaccinatum, herpes zoster, herpes simplex of the oral mucosa mostly on the hard palate, eczema herpeticatum, post-herpetic Erythema exsudativum multiforme, Mononucleosis infectiosa Pfeiffer, viral flu, German measles, parotitis epidemica, rubeola and ECHO-exanthema. A 5th and last group is made up by viral infections of other organs, in which affection of the oral mucosa hardly occurs at all. This group contains paravaccinal Ecthyma contagiosum, poliomyelitis, viral infection of the city of Marburg and some Arbovirus infections. Relatively few viral disorders never co-exist with lesions on the oral mucosa like e.g. Virus-hepatitis or some viral encephalitides. Groups 1 and 2, most important of all, are presented in detail regarding clinics, diagnostics, differential-diagnosis and therapy. The disorders within the other 3 groups are discussed only regarding their importance in the field of ENT-related symptoms of the oral mucosa. A number of pictures and tables completes important clinical details and give further hints to their differential-diagnosis.