Topically applied drugs which can cause contact dermatitis are numerous and diverse. The ingredients for vehicles, base components and additives, are as frequently the cause of drug eruptions as active ingredients. Patients with chronic leg ulcers are particularly exposed to the risk of developing allergic contact dermatitis. The diagnosis is based on the analysis of causative association between the localisation (often limited) of the lesions, the moment of their appearance and the application of a drug into the skin. Use tests and/or patch-tests are tools for determining the diagnosis. The exact knowledge of the offending ingredient, of its potential sources and the possibility of cross-allergy are essential in order to prevent recurrence. Indeed, the causative treatment of drug contact dermatitis is based on the prescription and effective application of strict avoidance of the causative allergen, a procedure which necessitates special informative measures to both the patient and to his medical care environment.