Objective. Total joint arthroplasty (TJA) places a significant economic burden on health care resources. This cohort study examines the costs associated with arthroplasty in 827 patients undergoing hip and knee TJA from January 2011 to June 2012 at a single center in Melbourne, Australia. Methods. Data included total inpatient, outpatient, and readmissions costs in the 30 days following TJA. Factors associated with cost were modeled using negative binomial regression and extrapolated to the Australian population. Results. The base cost (i.e., the cost for a patient with no modifying factors) over the first 30 days following TJA was 13,060 Australian (AU) (interquartile range 12,126?14,067 AU). The median length of stay was 4 days (range 2?33 days) and 35 patients (4 ) were readmitted in the first 30 days following index TJA, the majority of whom had a surgical site infection (SSI) (74 ). The following factors were independently associated with increased costs: SSI, preoperative warfarin therapy, American Society of Anesthesiologists score of 3 or 4, hip TJA, increasing operation time, increasing postoperative blood transfusion requirements, other nosocomial infections, postoperative venous thromboembolism (VTE), pressure ulcers, postoperative confusion, and acute urinary retention. Based on data from the present study, the cost of TJA in Australia is estimated to exceed 1 billion AU per year. Preventable postoperative complications were major cost drivers: SSI and VTE added a further 97 million AU and 66 million AU, respectively, to arthroplasty costs in the first 30 days following surgery. Conclusion. This unique study has identified important factors influencing TJA costs and providing guidance for future research and resource allocation.