Objective: To compare major reoperations in elderly patients with pertrochanteric and subtrochanteric fractures receiving a short versus a long intramedullary nail (IMN). Design: Multicenter cohort studySetting: Eleven orthopedic departments across Denmark delivered data from the Danish Multidisciplinary Hip Fracture Registry (DMHFR) and review of healthcare records.Patients: Using surgical procedure codes for pertrochanteric and subtrochanteric fractures treated with IMN, the DMRHF was used to identify patients over 65 years of age between 2008 and 2013.Outcome measures: Major reoperations, defined as any reoperation (simple hardware removal excluded), were retrieved from the DMHFR and all healthcare records were reviewed for type of IMN and missed reoperations, including peri-implant fractures, with 2 years of follow-up. Crude logistic regression and adjustment for age, sex, and comorbidity was performed, yielding odds ratios (ORs) with 95% confidence intervals.Results: Of 2,245 pertrochanteric fractures, 1,867 were treated with a short IMN and 378 were treated with a long IMN. There was a 4.0% rate of major reoperations in the short IMN group compared to a 6.4% rate in the long IMN group. This yielded a crude OR of 1.61 (1.01-2.60) and an adjusted OR of 1.67 (1.04-2.70).Of 909 subtrochanteric fractures, 308 were treated with a short IMN and 601 with a long IMN.The rate of major reoperations was 8.4% in the short IMN group and 4.0% in the long IMN group, yielding a crude OR of 0.45 (0.25-0.80) and an adjusted OR of 0.45 (0.25-0.81). Conclusion:This is the first study confirming the theory that, for subtrochanteric fractures, a long IMN has lower rate of major reoperations compared to a short IMN. In contrast, a short IMN has lower rate of major reoperations compared to a long IMN for pertrochanteric fractures but with a lower absolute risk reduction compared to subtrochanteric IMN results. There is a need for validation of these results in other large studies, especially for pertrochanteric fractures.