There are no data-supported recommendations on how proximal is too proximal for retrograde nailing (RGN). At six level 1 trauma centers, patients with femur fractures within the proximal one-third of the femur treated with RGN were included. This article describes a proximal segment capture ratio (PSCR) and nail segment capture ratio to evaluate RGN of proximal fractures. The study included 107 patients. The average follow-up was 44 weeks. There were two nonunions and three malunions. There was no significant difference between PSCR of 0.3 or less and need for secondary procedures or time to full weight bearing (p>.05). In this study, a smaller (< 0.3) PSCR was not associated with an increased number of complications. A higher Orthopaedic Trauma Association classification was predictive of malunion and increased time to union. These data demonstrate that retrograde nailing is safe and effective for the treatment of supraisthmal femur fractures.