The authors examine some specific forms of precancerous states of the oral cavity, selecting them from among the 4 classes defined by the WHO Collaborating Centre for Oral Precancerous Lesions. The immunological system is given particular emphasis. In fact, as studies progress, it appears to be more and more involved not only in the increase in the incidence of such pathologies, but also in the most difficult, if not unknown, genesis of these pathologies. Highly significant examples of this involvement are: Kaposi's Sarcoma, Hairy Cell Leukoplakia, Lichen and Mycoses. Particularly significant aspects for Erythroplasia consist in the following: slow development, frequent and rapid changes in the clinical aspects and its strict connection with Bowen's Disease and Queirat's Erythroplasia. The latter lend further confirmation of its definite precancerous nature and as such, it requires radical surgical treatment. Compared to other forms, the Epidemic variety of Kaposi's sarcoma more frequently affects the oral-salivary glands and structures, the lymph nodes and the laterocervical area. Together with non-Hodgkin tumors, this represents the class of neoplasms most frequently occurring in subjects affected by AIDS. Its "atypical" aggressiveness involves the liver and pancreas and develops over much shorter time periods than the other varieties. In any case, when possible, the treatment required is the excision of the lesions. Neither radiation therapy nor polychemotherapy have yielded encouraging results as yet. In the case of Leukoplakia, it should be kept in mind that today, this pathology is defined "negatively" be exclusion that is the condition must exist that this lesion cannot be clinically or pathologically defined as another lesion. It thus follows that the clinician must maintain an extremely cautious approach in such cases. As concerns prognosis, particular attention should be given to raised, hardened, irregular and fissured forms, which manifest the greatest degenerative capacity. for the classic forms, the treatment adopted is complete exeresis, whereas the use of antiviral drugs is recommended for Hairy Cell Leukoplakia. Lichen Ruber Planus is a papuliferous eruption that is relatively common and affects the skin and mucosa often exclusively involving the oral cavity in the great majority of cases. Besides the clinical picture, the diagnosis of this disease is based on the triad consisting of hyperkeratosis, destruction of the cells of the stratum basale and subepithelial lymphocyte infiltration at distinctly low levels. In uncertain cases, however, the detection of Fluorescent Bodies grouped in large clusters near the hyaline membrane, acquires particular importance for the specification of the diagnosis.