Objective: To present and interpret results of patch testing with the Mayo Clinic standard series over 5 years. Design: Retrospective study. A standardized patch testing technique was used. Data were recorded on a standardized computer program from January 1, 2001, to December 31, 2005, and analyzed. Setting: Tertiary referral center. Patients: Patients who were referred for patch testing. Intervention: Patch testing with the "standard series," ie, a standard series of allergens used by most clinicians to identify the most common offending allergens in patients with allergic contact dermatitis. Main Outcome Measures: Number of patients patch tested, allergens used over this period, and rates of allergic patch test reactions to allergens. Results: A total of 3854 patients (mean age, 55.1 years; age range, 6.2-99.4 years; 2576 female [66.8%]) were tested. All dermatologists in the department performed patch testing. The mean number of allergens included was 69.3 (range, 6-87). There were 2664 patients with at least 1 positive reaction (69.1%) and 1933 with 2 or more positive reactions (50.2%). Metals, fragrances, topical antibiotics, preservatives, and individual allergens used in hair-care products, topical corticosteroids, glues, plastics, and rubber were still the most common allergen groups associated with allergic patch test reactions. Conclusions: We describe the structure of the patch testing service at our referral center. Ongoing analysis of our patch test reaction rates allows us to recommend broad, clinically relevant, and up-to-date allergens for testing.