Background. The occurrence of a new skin disorder exactly at the site of another one, already healed and unrelated, was first described in 1955. In 1985, Wolf et al. recognized that we are dealing with a dermatologic phenomenon and established a precise definition for this phenomenon. Fifty‐eight cases corresponding to the definition of this phenomenon have been reported until now. Methods. The new phenomenon, for which the term “isotopic response” has been suggested, has been defined. Cases corresponding to the definition have been analyzed with special emphasis on the diseases involved, the time intervals, and the locations of the diseases. Eight new cases are described. Results. A total of 58 cases of isotopic response have been described. The first disease in most of the patients was herpes zoster; in three cases it was herpes simplex, in two varicella, and in one, thrombophlebitis. The second disease, which appeared exactly at the site of the first, already healed disease, was in most reported cases a carcinoma (26 cases, in particular 15 cases of breast carcinoma, 5 basal cell carcinomas (BCC), 4 squamous cell carcinomas (sec), 2 basosquamous carcinomas), or granuloma annulare (16 cases). Additional diseases were Kaposi's sarcoma (2 cases), pseudolymphoma (2 cases), sarcoid (2 cases), tinea (2 cases), tuberculoid and vasculitis granuloma (1 case), angiosarcoma, metastasis, Bowen's disease, lymphoma, leukemia cutis, and acne (1 case each). The diseases did not show any predilection for a particular location. The interval between the first and second disease was extremely variable (ranging from days to years) and showed no particular features. In the eight additional cases described in the present report, the first disease was herpes simplex (6 cases) or herpes zoster (2 cases). The second disease was viral warts (3 cases) or squamous cell carcinoma (2 cases). Additional diseases were furunculosis, contact dermatitis, and molluscum contagiosum (1 case each). Conclusions. The new term, “isotopic response,” describes the occurrence of a new skin disorder at the site of another, unrelated, and already healed skin disease. It is suggested that the term “isotopic response” be included in the lexicon (glossary) of dermatology. Introducing the new term and classifying all the cases under a single key word, will make it possible to locate and collect them easily and to search for the mechanism underlying this phenomenon.

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