Introduction: Malnutrition is considered a risk factor for post-operative complications in total hip and knee arthroplasty, though prospective studies to investigate this assumption are lacking. The aims of this study were to prospectively analyze the 90-day post-operative complications, post-operative length of stay (LOS), and readmission rates of patients undergoing primary total hip and total knee arthroplasty using albumin, total lymphocyte count (TLC), and transferrin as serum markers of potential malnutrition. Materials and Methods: Six hundred and three primary hip and 823 primary knee arthroplasties over a 3-year period from a single center were prospectively analyzed. Body mass index, demographic, and comorbidity data were recorded. Complications were categorized as surgical site infection (SSI), venous thromboembolism (VTE) (deep vein thrombosis and pulmonary embolus), implant-related (such as dislocation), and non-implant-related (such as pneumonia). Outcomes were compared between groups, with malnutrition, defined as serum albumin <3.5 g/dL. Results: Potential malnutrition was present in 9.3% of the study population. This group experienced a longer average LOS at 6.5 days compared to the normal albumin group at 5.0 days (P = 0.003). SSI rate was higher in the malnourished group (12.5 vs. 7.8%, P = 0.02). There was no difference between the two groups in implant-related complications (0.8 vs. 1.0%, P = 0.95) medical complications (7.8 vs. 13.3%, P = 0.17), rate of VTE (2.3 vs. 2.7%) or 90-day readmission rate (14.1 vs. 17.0%, P = 0.56). TLC and transferrin were not predictive of any of the primary outcomes measured (P > 0.05). Pacific Island (P < 0.001), Indian (P = 0.02), and Asian (P = 0.02) patients had lower albumin than NZ European. Conclusion: This study demonstrates an association between low albumin levels and increased post-operative LOS and SSI in total joint arthroplasty, providing support for the consideration of pre-operative nutritional screening. Keywords: Knee arthroplasty, hip arthroplasty, malnutrition, post-operative complications, hypoalbuminemia.