Open lower limb fractures are resource-intensive fractures, accounting for a significant proportion of the workload and cost of orthopaedic trauma units. A recent study has evaluated that the median cost of direct inpatient treatment of open lower-limb fractures in the National Health Service (NHS) is steep, at £19189 per patient. Healthcare providers are expected to be aware of the costs of treatments, although there is very limited dissemination of this information, neither on a national or local level. Older adults (>65 years old) are at an increased risk of the types of high-energy injuries that can result in open lower limb fractures. Generally, there remains a significant lack of literature surrounding the cost of open fracture management, especially in specific patient groups that are disproportionately affected by these fractures. This study has calculated the direct inpatient care costs of older adults with open lower limb fractures. Open lower limb fractures in adult patients over 65 years old treated at Addenbrooke's Hospital of Cambridge University Hospitals NHS Trust were identified over the period of March 2014-March 2019. Isolated fractures of the femur, tibia and fibula over this time period were included. Direct inpatient care costs were calculated using information about the sustained fracture, operative time, implant(s) and theatre kit(s) used, the number of patient bed-days on the orthopaedic ward and critical care unit, and the number of hours of inpatient physiotherapy received. Direct inpatient care costs were compared with the income received by our centre for each of these cases, according to Healthcare Resource Group (HRG) cost codes. Our data was also compared with existing literature on Patient Level Costing (PLC) figures for open lower limb fractures. We extracted data from 58 patients over the age of 65 years treated for open isolated lower limb fractures at Addenbrooke's Hospital, Cambridge University Hospitals NHS Trust, between March 2014 and March 2019. The median cost of inpatient care calculated in this study was £20,398 per patient, resulting in a financial loss to the hospital of £5113 per patient. When the results were disaggregated by sex, the median cost for an open lower limb fracture in a male patient was £20,886 compared to £19,304 in a female patient. Data were also disaggregated by the site of injury, which produced a median cost for an open femur fracture of £23,949, and £24,549 and £15,362 for open tibia and ankle fractures, respectively. The absence of published primary literature and clinical audits on this topic continues to hinder the inclusion of cost-effectiveness as an important factor in clinical decision-making. This study provides valuable insight into the true cost of open lower limb fractures in a key patient population in a Major Trauma Centre in England and highlights the large losses incurred by hospitals in treating these cases. These results support the revision of the remuneration structures in the NHS for the treatment of elderly patients with these injuries