BACKGROUND: We aimed to investigate the effect of bone morphology on fracture type and treatment result in patient with inter- trochanteric fracture (IFF) treated with intramedullary nailing (IMN) aged over 65 years. Primary outcome of study was to investigate the relationship between fracture type (stable or unstable) and bone density. METHODS: This was a retrospective cohort study conducted at single trauma center which included patients aged >65 years, mini- mum 3 months’ control postoperatively, patients with simple fall by evaluating the patient data from 2010 to 2021. All fractures were classified based on the AO classification system. Proximal femoral nail anti-rotation was used between 2010 and 2016, while InterTAN was used after 2016 in our clinic practice. For the evaluation of the bone morphology, we measured the canal-to-calcar ratio (CCR) and cortical thickness index (CTI) and classified with Dorr morphology on anteroposterior (AP) hip radiograph of both the fracture side and contralateral sides. Complications were also evaluated on radiological view. Failures were defined as non-union or failure of fixation. Excessive collapse and screw/blade prominence also evaluated by hip radiograph on the 3rd month control visit. RESULTS: One hundred and fifty females and 59 males were included in this study. The average age was 81.6±8.8 years. One hundred and forty-four patients were treated with InterTAN and 65 patients with helical blade type IMN (PFN-A®). There were 78 patients with stable IFF type A1 fracture and 131 patients with unstable IFF (109 patients with A2 and 22 patients with A3 AO type fracture). The mean CTI was 0.469±0.09 and 0.510±0.09 in the fracture and unaffected side femurs, respectively (p<0.001), the CCR was 0.636±0.15 and 0.568±12 in the fracture and unaffected side femurs, respectively (p<0.001). There were 36 patients with Dorr type A, 115 pa- tients with Dorr type B, and 48 patients with Dorr type C in fracture side and 65 patients with Dorr type A, 123 patients with Dorr type B, and 21 patients with Dorr type C in non-affected side (p<0.001). There were 29 (13.9%) patients with screw (n=14) and blade (n=15) prominence. Excessive collapse was seen 30 patients (14.4%) and 16 patients (7.7) evaluated as a failure. CONCLUSION: We found a significant difference in the failure rate between unstable group than stable group which higher in unsta- ble group according to the AO classification. In addition, the mean CTI, CCR, and Dorr index were significant difference in fractured side than unaffected side which indicated lower bone quality at fracture side.