Malnutrition can increase the risk of surgical site infection in both elective spine surgery and total joint arthroplasty. Obesity and diabetes are common comorbid conditions in patients who are malnourished. Despite the relatively high incidence of nutritional disorders among patients undergoing elective orthopaedic surgery, the evaluation and management of malnutrition is not generally well understood by practicing orthopaedic surgeons. Serologic parameters such as total lymphocyte count, albumin level, prealbumin level, and transferrin level have all been used as markers for nutrition status. In addition, anthropometric measurements, such as calf and arm muscle circumference or triceps skinfold, and standardized scoring systems, such as the Rainey-MacDonald nutritional index, the Mini Nutritional Assessment, and institution-specific nutritional scoring tools, are useful to define malnutrition. Preoperative nutrition assessment and optimization of nutritional parameters, including tight glucose control, normalization of serum albumin, and safe weight loss, may reduce the risk of perioperative complications, including infection.