The Gruppo Italiano Ricerca Dermatiti da Contatto e Ambientali (GIRDCA) resolved to obtain the most relevant data regarding contact dermatitis (CD) in Italy by means of a multicenter epidemiological study, involving research units (RU) throughout the country. The survey was performed with the collaboration of Generale Per l'Informatica, Rome (GEPIN) over the periods 1984 to 1988 and 1989 to 1993. The analytical study (of a transverse kind) was aimed at supplying prevalence measures. The number of subjects taking part in the survey was 42,839. All patients underwent patch testing with the GIRDCA standard series and were included in the survey only if the final diagnosis was either CD or eczematous dermatitis caused by contact. The main anamnestic, clinical data, and allergological test results of all patients were codified into a chart, and subsequently transcribed into a data bank. The data were then processed cumulatively and were statistically analysed by a chi-square for trend test. The four most frequent diagnoses (which, when considered together, make up 39,496 cases, or about 92% of all cases) proved to be nonoccupational allergic contact dermatitis (ACD), nonoccupational irritant contact dermatitis (ICD), occupational ACD, and occupational ICD. The haptens most frequently causing positive reactions in the total number of cases over the first 5 years were, in order of frequency: nickel sulphate, potassium dichromate, cobalt chloride, fragrance mix, balsam of Peru, and, in the second 5-year period, nickel sulphate, cobalt chloride, potassium dichromate, fragrance mix, and thimerosal. Occupational CD (ACD and ICD) was present in 11,694 cases overall, corresponding to approximately 27% of the total number of cases examined, and approximately 29% of all CD (including forms of nonoccupational CD). Regarding distribution by sex, a substantial equivalence of males and females for ACD, and a prevalence of females with ICD can be observed. Five occupations were reputed to be responsible for over 60% of total cases of occupational CD (housewives, bricklayers, workers in the metallurgic and mechanical industries, hairdressers, and healthcare personnel). Regarding the pathogenesis, a clearly dominant percentage of ACD may be observed among bricklayers and hairdressers, and of ICD among housewives. The haptens most frequently noted over the entire decade as the cause of positive reaction in occupational ACD were, in order of frequency, potassium dichromate, nickel sulphate, cobalt chloride, p-phenylenediamine and thiuram mix. Nonoccupational CD (ACD and ICD) was present in 27,802 cases overall, corresponding to about 65% of all cases under examination and over 70% of all CD (also including forms of occupational CD). In regard to distribution by sex, a clear dominance of females, as opposed to males, can be noted for ACD and also (although to a lesser extent) for ICD. The main products and materials (ie, components and relative substances) that are pinpointed as being responsible for nonoccupational ACD, were, in order of frequency, clothing accessories, cosmetics, topical pharmaceuticals, and clothing. The haptens most frequently recognized as the cause of positive reactions were, in order of frequency, nickel sulphate, fragrance mix, cobalt chloride, balsam of Peru, potassium dichromate, ethylenediamine, and diaminodiphenylmethane.