OBJECTIVES: Patch testing is a well-established method to determine whether contact sensitization to certain agents has occurred and it can directly influence the clinical outcome of patients with allergic contact dermatitis (ACD) where detection of causative allergens is crucial for appropriate prevention and treatment. Its positive predictive value, however, is influenced by many variables. In particular, not all patients referred for patch testing actually have ACD and not all positive reactions are clinically relevant. The objective of our study was to develop an outcome indicator of patch testing. METHODS: We identified and measured as a possible indicator the ratio of patients with allergic and/or photo-allergic contact dermatitis clinically cured/improved as a result of identification of relevant allergens.  Patients with positive reactions considered relevant to their current dermatitis were interviewed by telephone 2 months after patch/photo-patch testing in order to assess their clinical outcome in relation to the recommended elimination of supposedly relevant allergens. We parallely evaluated the prevalence of referral diagnosis different from ACD in patients whose test results were negative/non-relevant. RESULTS: Over a 4-year period positive reactions were seen in 1397 out of 2857 tested patients. Relevance was considered current in 578 subjects, and 506 of them were interviewed. Remission/significant improvement following allergen(s) contact avoidance was reported by 431 patients, the outcome indicator (431/506) thus scoring 85.2%. Among the 75 patients who reported no improvement, 41 had not avoided contact with the offending substance(s), 17 had other persistent concomitant skin conditions, and 17 were unchanged despite elimination of the alleged relevant allergens. The likely diagnoses of patients whose test results were negative/non-relevant were: non-eczematous diseases (39% of total patients), endogenous eczema (22%), irritant contact dermatitis (10%),  unknown (5%), possible ACD from unidentified haptens (4%). CONCLUSIONS: The ratio of relevantly patch-test-positive patients resolved/improved after allergen avoidance is a useful patch-testing outcome indicator