There is experimental evidence that vitamin A-deficiency plays a role in tumorigenesis. Therefore, vitamin A was used in the treatment of malignant tumors. Unfortunately, it was found that the compound was too toxic and therefore its clinical usefulness was limited. Chemical modifications of the vitamin A molecule lead to what is now called the retinoids, which in general show higher efficacy and better tolerance than vitamin A itself. In this article some of the retinoids like 13-retinoic acid (Roaccutan) and etretinate (Tigason) are described with regard to their antitumor activity in animals and man. In widespread malignant disease the efficacy so far is limited to patients with basal cell carcinoma and mycosis fungoides. However, in the treatment of premalignant or in the prevention of recurrent disease retinoids have found much broader application. This is demonstrated by the successful treatment of several diseases like oral leukoplakia, actinic keratosis, xeroderma pigmentosum, bronchial metaplasia and superficial bladder carcinoma.