Background: Type I insulin allergy can be a challenging condition, and there is no international consensus on how to establish the diagnosis. Measurement of specific IgE and skin testing have been cornerstones in the diagnostic work-up. However, these tests have limitations, mainly lack of correlation between test results and clinical findings. At the Allergy Centre, Odense University Hospital, patients with suspected insulin allergy have been evaluated since 2003. The aim of this study was to establish a systematic approach to diagnose and treat patients with insulin allergy. Methods: The study was conducted retrospectively by retrieving data from the Allergy Centre database on patients with suspected insulin allergy evaluated from 2003 to 2017. The examination comprised a comprehensive medical history, specific IgE against insulin and intracutaneous tests (ICT) with different insulins. Results: A total of 144 patients were examined on suspicion of insulin allergy of which 110 had negative specific IgE in serum. Of the remaining 34 patients, 33 had ICT performed; 2 had negative ICTs, while 31 had one or more positive ICT. All 34 patients had mild symptoms, and 4 could obtain symptom relief with antihistamines or local steroids, 9 could be managed with oral antidiabetics, and 7 were switched to other insulins. The final 14 patients were offered an insulin pump because of reactions to many different insulins, many positive ICTs, unmanageable diabetes, young age and compliance, or convenience. Conclusion: Insulin allergy can be managed by a systematic approach, and symptom relief is obtainable in most patients.