Elderly patients with lower-extremity fractures are at high risk of postoperative pneumonia (POP) after surgery due to longtime bed rest. This study aimed to explore whether preoperative frailty is an independent risk factor for POP in elderly patients undergoing surgical treatment for lower-extremity fractures. The study adopted a cross sectional design with 568 patients (≥60 years) admitted to a tertiary hospital in China from January 1, 2021 to June 30, 2022, for surgical intervention of a significant lower-extremity fracture. Preoperative frailty was assessed using the CFS (Clinical Frailty Scale). POP was assessed based on the classic diagnostic criteria reported in previous studies. Univariate and multiple logistic regression analyses were conducted to determine the impacts of preoperative frailty on POP. Of the 568 elderly patients, 65 (11.4%) developed pneumonia during postoperative hospitalization. There were significant differences among gender, hypoproteinemia, type of anesthesia, history of chronic obstructive pulmonary disease (COPD), and CFS scores. Multiple regression analysis revealed that the risk of POP in vulnerable, mildly frail, and severely frail patients increased by 2.38 times (
P
= .01, 95% CI [1.22–1.91]), 3.32 (
P
= .00, 95% CI [2.39–5.61]), and 5.36 (
P
= .00, 95% CI [3.95–6.52]), significantly. 12.8% of patients with hip fractures and 8.9% of patients with other main types of lower-extremity fractures developed POP. However, the difference between hip and non-hip fractures was not statistically significant (
P
> .05). Preoperative frailty increases the risk of POP in elderly patients after surgical treatment of main lower-extremity fractures. The severer the preoperative frailty is, the higher the risk of preoperative pneumonia is in elderly patients with lower-extremity fractures. CFS is simple and feasible for the assessment of frailty in elderly patients with lower-extremity fractures. Preoperative frailty assessment and appropriate management strategies should be considered in the perioperative management of elderly patients with lower-extremity fractures.