Background: In elderly patients with femoral neck fracture, functional recovery is affected largely by preoperative underlying diseases and postoperative complications. The present study was designed to analyze the relationship between preoperative underlying diseases and perioperative complications of surgery for proximal femur fracture. Methods: The study involved 86 patients aged 75 years or older, who underwent surgery for proximal femur fracture. Each patient was examined for the presence of preoperative underlying diseases and preoperative biochemical test data. Moderate and severe complications, which were life-threatening and necessitated treated, were investigated during the perioperative period. A retrospective analysis was conducted on the relationship of preoperative underlying diseases and preoperative biochemical data with the moderate or severe complications that developed during the perioperative period. Results: Eighty-one patients developed a preoperative underlying disease, with hypertension being most frequent (42 cases). Complications during the perioperative period were observed in 58 patients, with anemia develops most frequently (23 cases). Moderate or severe complications during the perioperative period were observed in 16 patients, and infection was the most frequent complication (8 cases). In the statistical analysis, a significant difference in the incidence of moderate or severe perioperative complications was observed only in the users of anticoagulants/antiplatelet drugs. Discussion: Patients of preoperative use of anticoagulants/antiplatelet drugs should be closely managed medically so that perioperative medical complications can be managed.