During the ten year period 1953-1962, a total of 12,955 in-patients were treated in the Department of Dermatology, Rikshospitalet, Oslo, and 2,253 of them were diagnosed as eczema idiosyncraticum (allergic contact dermatitis). Two-hundred eighteen (9.7%) of these cases of allergic contact dermatitis were believed to have contracted their dermatitis through allergy to formaldehyde in clothing. The incidence of formaldehyde clothing dermatitis in this series has shown a remarkable increase from 1.9% of the annual number of allergic contact dermatitis cases in 1953 to a maximum of 23.1% in 1961. Of the 218 patients, 163 were females and 55 males, the ratio for females to males being approximately 3 to 1. The incidence of formaldehyde clothing dermatitis is compared with that of clothing dermatitis from allergy to dyes during the same period. It is concluded that formaldehyde amine resins, particularly formaldehyde melamine and formaldehyde urea, may gradually depolymerize while in contact with human skin. Free formaldehyde thus released is capable of causing allergic contact dermatitis. This depolymerization seems to be facilitated by sweat and the higher temperature of the flexures. The climacteric, psychic conflicts and other nervous factors are thought to have some influence on the liability of human skin to break down formaldehyde resins in clothing. This may explain why some individuals, who are allergic to formaldehyde, contract this type of clothing dermatitis while other formaldehyde sensitive patients do not. Unknown constitutional factors, racial, nutritional, and climatic circumstances may also be of importance, and might explain why this "Scandinavian epidemic" of formaldehyde clothing dermatitis is not encountered in some other countries. Schiff's reagent for detection of aldehydes is useful in testing patients' garments in order to exclude from their wardrobe textiles capable of releasing formaldehyde.