PURPOSE: Postoperative radiographs are routinely used to assess fracture reduction following intramedullary nail fixation for pertrochanteric fractures, even though computed tomography (CT) is a superior modality. We aimed to determine the association between reduction quality assessed by CT and rates of reoperation and to evaluate the association of reoperation and reduction quality according to the assessment modality (plain radiographs vs. CT). METHODS: A retrospective analysis of 299 consecutive patients treated with intramedullary nail fixation for pertrochanteric fractures was conducted. Fracture reduction measured by postoperative radiographs and CT was categorized as anatomical type, extramedullary type, or intramedullary type. Postoperative data for analysis included reduction status, tip-apex distance (TAD), screw position in the femoral head, sliding distance, and conditions associated with reoperation. RESULTS: Of the 299 patients included with a mean age of 83.1 ± 8.2 years, there were six patients who required reoperation (2.0%). According to the CT assessments, there were 42 intramedullary reductions (14.0%). Patients with a non-intramedullary reduction based on postoperative CT images were significantly more likely to have proper placement of the screw, a reduced TAD, a reduced sliding distance, and a lower reoperation rate than those with an intramedullary reduction (P < 0.05). The reduction quality assessed by postoperative CT was significantly associated with reoperation (95% CI, 1.45-29.31). CONCLUSIONS: Intramedullary reduction assessed by CT was associated with reoperation. The reduction quality based on CT findings was more predictive for reoperation than that from plain radiographs.