Background: American Society for Bone and Mineral Research recommend the use of intramedullary reconstruction of full length-nail for atypical subtrochanteric femoral fracture (ASFF). However, there is no study on the incidence of the ipsilateral femoral fracture after index operation of ASFF, and full-length nail has disadvantage as iatrogenic fracture and leg length discrepancy (LLD). The aim of this study was to investigate the incidence of ipsilateral secondary fracture after using partial-length nail, and to compare the outcomes on surgery of ASFF between partial length-nails and full length-nails. Methods: Forty-five consecutive fractures with ASFFs which had undergone intramedullary fixation using cephalomedullary nail between 2011 and 2018 were enrolled. The 45 cases were grouped based on nail length into the partial-length nail group (n =26) and the full-length nail group (n=19). Ipsilateral secondary fracture, time to union, intraoperative iatrogenic fracture, metal failure, LLD, operative duration, and post-operative 24-hr blood loss were investigated. Results: There was no ipsilateral secondary fracture after index operation. There were no statistically significant differences between the partial-length nail and full-length nail groups in the time to union, LLD, and post-operative 24-hr blood loss (P=0.427, 0.478, and 0.228, respectively). Operative duration showed statistically significant difference between 2 groups (P=0.034). Metal failure were occurred in 1 (3%) case of the partial-length nail group and 2 (10%) cases of the full-length nail group. Iatrogenic fractures during nail insertion occurred in 2 (7%) cases of the partial-length-nail group and 3 cases (15%) of the full-length nail group. Conclusions: Although large scale studies are required, our study indicate that full-length nails are not usually required for the treatment of ASFF.