Acute kidney injury (AKI) is a recognised postoperative complication following primary hip/knee arthroplasty surgery. The aim of this study was to determine causative and potentially modifiable risk factors associated with postoperative AKI. Standard data were collected for 413 consecutive arthroplasty patients, both retrospectively and prospectively. Univariate and multivariate analyses were performed to identify any potential causative factors. Eight percent of patients developed postoperative AKI. Univariate analysis found increasing age, history of previous chronic kidney disease and requirement for postoperative intravenous fluids to be risk factors for AKI. The multivariate regression analysis model identified age and volume of postoperative fluid prescription as predictive of postoperative AKI. Antibiotic regime and prescription of non-steroidal anti-inflammatory drugs had no significant effect on the risk of AKI. No patients required dialysis but length of stay increased by 50% in the AKI group. Postoperative AKI may result in significant postoperative morbidity and increased length of stay, and may necessitate invasive therapies such as dialysis. Episodes of AKI could also predispose to future similar episodes and are associated with a long-term decrease in baseline renal function. This study has demonstrated that the identified risk factors are generally non-modifiable. Further work is suggested to determine whether targeted interventions in high risk patients would reduce the incidence of AKI.