A multicenter study was performed in 12 Italian medical centers by members of Gruppo Italiano Ricerca Dermatiti da Contatto e Ambientali (GIRDCA) over 5 years (January 1984 to December 1988) to set up a computerized data bank on contact dermatitis. With a subsequent analytical study, the significance of trends of individual data was computed by using the chisquared test and a linear regression analysis. As to the distribution of the population under review (23,541 cases) in relation to the etiology, nonoccupational causes turned out to be responsible for contact dermatitis (CD) in more than 60% of cases, and, according to the pathogenesis, more than 60% of CDs are allergic contact dermatitis (ACD). Occupational ACD tends to decrease significantly and, on the contrary, tends to increase with time in cases of nonoccupational irritant contact dermatitis (ICD). In occupational CD after an initial prevalence of the allergic pathogenesis, irritation takes over while among nonoccupational forms allergics still clearly prevail. Clothing accessories made of metal and costume jewelry (39.6%), cosmetics (29.3%), medicaments (14.6%), and clothing (9.4%) are the main etiological factors in nonoccupational ACD. In the workplace, five professions (housewives, construction workers, workers in the metallurgical and mechanical industries, hairdressers, and health care providers) cause more than 60% of the cases of CD. The total values and percentages of positive reactions to patch tests for occupational and nonoccupational ACD manifest significant changes in time for some haptens, in particular, a trend toward an increase in nickel sulphate and wool alcohols and a decrease in thiuram mix, neomycin, p-phenylenediamine (PPD), Peru balsam, ethylenediamine, formaldehyde, and carba mix.