In the United States, \~1 million elective hip or knee replacement surgeries are performed annually. With estimated surgical site infection (SSI) rates as high as 2.5%, this represents \~25,000 patients at risk of potentially avoidable morbidity following lower extremity joint replacement surgery. Although SSIs only account for 20% of all HAIs, they are a major risk factor for prosthetic joint infections (PJIs). Furthermore, UTIs have also been identified as an independent risk factor for infections of implanted hardware. In general, the majority of PJIs become apparent within 3 months of hardware implantation, but deep infections may not be evident for up to one year after surgery. Hardware infections result in delayed healing, repeated surgical interventions, and long-term antibiotic therapy. PJIs are associated with an average increase in hospital LOS by 14 days, additional expenditures of up to $50,000 per infected joint, and a doubling of the mortality rate compared to uninfected lower extremity joint replacements. Recent work from our group suggests that vitamin D insufficiency may be a risk factor for perioperative HAIs. The prevalence of vitamin D insufficiency is approximately 40% in elective joint replacement surgery patients, and perioperative 25(OH)D levels drop 30-40% in the setting of surgical stress, remaining 20% below baseline up to 3 months after surgery. To date, perioperative vitamin D optimization strategies have not been reported. Therefore, our goal is to study the effect of a single (pre-operative) versus a divided (pre-operative and on post-operative day 1) dose of cholecalciferol on perioperative vitamin D status in patients scheduled for elective hip or knee joint replacement surgery.