As the aging population progresses, the number of elderly hip fracture patients is increasing. Elderly patients with hip fractures have a high risk of perioperative complications. One of the major complications after surgery is surgical site infection (SSI), which requires additional surgical interventions and is associated with increased mortality. Previous literature has shown that the risk of SSI is higher during the summer season in orthopedic surgery. However, little is known about the seasonal differences in the risk of SSI after hip fracture surgery. In this study, we aimed to identify the association between seasonality and SSI. We enrolled a total of 330,803 patients undergoing hip fracture surgery (65 years or older) using the Japanese Diagnosis Procedure Combination database. The study period was from April 1, 2011, to March 31, 2016. The data were analyzed to determine the association between seasonality and the incidence of SSI, debridement procedure. The primary outcome was the incidence of SSI and debridement. Other risk factors of SSI and debridement were investigated including seasons and confounders such as sex, age, BMI, smoking status, anticoagulant intake, comorbidities, surgical procedure based on medical diagnosis, waiting times for the surgery, and hospital surgical volume based on the previous literature, the risk of SSI and debridement. Hip fracture surgeries performed in summer showed the highest risk for SSI and debridement. The risk for SSI was significantly associated with spring, and summer compared to winter (odds ratio [OR], 1.18; p, 0.016; OR, 1.19; p, 0.012, respectively). The incidence of debridement procedures after the initial surgery was also associated with spring, summer, and fall: the risk was the highest in summer (OR, 1.34; p, <0.001). Obesity, smoking history, number of comorbidities, anticoagulant intake before surgery, longer waiting time for surgery, and small hospital surgical volume were significantly associated with the risk of SSI. We found a significant association between SSI after surgery for hip fractures and seasonality. Surgeries performed in summer had the highest risk for SSI and subsequent debridement procedures. Copyright © 2020. Published by Elsevier Ltd.