Fifty dermatology departments from Germany, Austria and Switzerland collaborate to study the clinical epidemiology of contact allergies (CA). Data generated in the course of the diagnostic work-up of CA (e. g. patch test data) are stored since 1989 in the data centre in Gottingen, amounting to more than 170 000 patients (August 2008). These data can be used as a register, and as a surveillance system. Analysis of the register may identify and quantify risk factors of sensitization to an allergen, which is exemplified with the case of the aminoglycoside antibiotics. It turned out that kanamycin is associated with a higher risk of sensitization than gentamicin. In contrast, data collected every 6 months (from -6000 patients) allow for time trend analyses of allergens, thus identifying allergens of concern, which is of utmost importance for early preventive intervention. Here, the epidemiology of allergies to fragrances and other allergens serve as examples. Continuous monitoring of contact allergens will also be mandatory in future, as the CA pre-marketing screening systems will have imperfect predictive values with regard to human CA risk.