Background: The current standard tool for diagnosing allergic contact dermatitis (ACD) in the United States is the T.R.U.E. test panels, which consist of 23 allergens. Previous studies have raised concern regarding the adequacy of these panels in fully assessing patients with possible ACD. Objective: We sought to examine the use of the T.R.U.E. test allergens as the primary diagnostic method for detecting ACD. Methods: A retrospective analysis of all patients with possible ACD who presented to the University of Kansas' Section on Occupational and Contact Dermatitis in Kansas City, Kansas, and subsequently underwent patch testing from January 1, 1995, to December 31, 2001. Patients with positive allergic reactions were stratified into 3 groups: (1) reactions only to allergens on the T.R.U.E. test; (2) reactions only to allergens not present on the T.R.U.E. test; and (3) reactions to allergens on the T.R.U.E. test and additional allergens. These 3 groups were further analyzed to assess clinical relevance. Results: Of the 898 patients who were patch tested, 616 (68.6%) had at least 1 positive allergic reaction. Among these 616 patients, 25.5% would have been fully evaluated using the T.R.U.E. test allergens only. Of the remaining patients, 22.4% would not have had any of their allergens detected and 52.1% would have only been partially evaluated had only the T.R.U.E. test allergens been used. Similar percentages were observed when only patients with clinically relevant reactions were included. Conclusions: In our study, the current T.R.U.E. test series of 23 allergens would have completely identified all allergens in only 25.5% of patients and clinically relevant allergens in 28% of patients. Expanding the number of allergens used according to a patient's environment and history will lead to improved outcome in the treatment and prevention of ACD. (J Am Acad Dermatol 2003;49:65-9.)