The incorrect use of the terms vitamin overdosage and overload, hypervitaminosis and dysvitaminosis gives rise to errors in the classification and evaluation of their etiology and pathogenesis. Vitamin overdosage and overload are observed with every vitamin and produce high blood and tissue levels of the vitamin itself; however, the overdosage can be obtained only upon administration of high doses of a vitamin, while vitamin overload may originate from a variety of factors. Hypervitaminoses are known for vitamin A and D; they are accompanied by high blood levels, but are characterized by a specific symptomatology. The term dysvitaminosis comprises "every alteration of the physiological status of the vitamin, in terms of both its deficiency and its surplus". These considerations provide a unitary view of vitamin pathology and lead to the following proposal of an etiopathogenetic classification of dysvitaminoses: class A) dysvitaminoses due to overload, class B) dysvitaminoses due to deficiency. Each class in turn may be divided into congenital and acquired syndromes. In class A) the congenital syndromes are still not well known, the acquired syndromes comprise those with hypervitaminosis (hypervitaminosis A and D) and those without hypervitaminosis (for the other vitamins). In class B) the congenital syndromes comprise diseases produced by inborn enzymatic errors and by other etiologies, the acquired syndromes can be distinguished in physiological (age, pregnancy, etc.) and pathological (nutritional, iatrogenic, etc.) ones. On this basis hypervitaminoses A and D can be considered as non obligatory dysvitaminoses due to overload; their origin has a complex etiology, since the liposolubility of the vitamins and the prolonged use of high dosages are not the only factors responsible for the hypervitaminosis.