BACKGROUND: Multiple drug hypersensitivity syndrome (MDHS) is defined as confirmed drug hypersensitivity (DH) to at least 2 chemically and pharmacologically unrelated drugs. Reports of MDHS are scarce and poorly specified, and studies that diagnose MDHS on the basis of positive allergy test results are lacking. OBJECTIVE: To evaluate retrospectively the frequency and characteristics of patients with MDHS in a large database. METHODS: We included all patients who consulted and were tested in our Allergy Unit between September 1996 and February 2018 for a suspicion of DH. Clinical history and allergy workup results compiled in our Drug Allergy and Hypersensitivity Database were reviewed, and data of patients with a diagnosis of MDHS were retrieved and analyzed. RESULTS: During this period a total of 9250 patients were explored and 1819 tested positive for at least 1 drug. Forty-five cases, 30 female and 15 male patients cumulating 92 DHs, were confirmed as having MDHS. An immunologic mechanism, as demonstrated by positive skin testing, accounted for 59 DHs. Drug provocation tests were performed to confirm the diagnosis for the remaining 33 DHs. Of the 92 DHs in this series, 38 were classified as type IV and 21 as type I allergies; 33 remained of undetermined mechanism. Drug class occurrences seem to differ from those in monoallergic patients. CONCLUSIONS: Our data support the concept of MDHS as a distinct and rare subgroup of DH. The prevalence in our database was 2.5% in the total DH alleged patient population and 0.5% of the demonstrated DHs. Skin testing and drug provocation tests are mandatory for confirming the diagnosis. (C) 2019 American Academy of Allergy, Asthma & Immunology