Objective: To present a case study demonstrating an atypic side effect of insulin — hepersensitivity reaction to insulin detemir, a long-term human insulin analogues. Key Points. At the inpatient paediatric unit, we had an 11-year old girl with symptoms and clinical signs of diabetes mellitus (DM). Following physical examination, the patient was diagnosed with type 1 diabetes (manifestation). She was prescribed intensified basal-bolus therapy with insulin analogues: insulin detemir and insulin aspart. On day 5, the patient developed a hypersensitivity reaction in the site of insulin detemir injections. Replacement of insulin detemir with insulin degludec resolved the allergic reaction. Conclusion. We described a case of a hypersensitivity reaction to intensified insulin therapy with basal insulin analogue detemir. Hypersensitivity reactions to insulin analogues are rare; however they can be life-threatening. The primary management is the use of another insulin analogue. Keywords: diabetes mellitus, allergy, insulin detemir, insulin degludec.