BACKGROUND: We assessed risks of incident in-hospital complications and 1-year and 5-year mortality following elective primary total joint replacement (TJR), focusing on obesity. METHODS: Longitudinal data from a population-based cohort of 819 men who had had TJR were integrated with validated hospital morbidity data and mortality records. Complications recorded in the index admission were classified as major or minor by 13 independent orthopaedic surgeons. RESULTS: Of 819 men (mean age 76.3 (SD 4.5) years), 331 patients (40.4%) had an in-hospital complication from whom 155 (18.9%) had at least one major complication that was classified as potentially life threatening. Obesity and age were independently associated with increased risk of major complications. Compared with patients without complications, those with major complications experienced significantly greater mortality in 1 year (5.8% versus 1.2%, P = 0.001) and 5 years (16.8% versus 8.0%, P = 0.002) following TJR. In Cox regressions, age, Charlson Co-morbidity index and major complications were independently associated with 1-year mortality. Age and Charlson Co-morbidity index were also associated with 5-year mortality. Similarly, risk of dying within 5 years of TJR was higher among patients with class II obesity compared with patients with normal weight. The most frequently reported complications were those in the cardio-respiratory and general systems. Complications in the cardio-respiratory system significantly increased hazard of 1- and 5-year mortality. CONCLUSION: The elderly and the obese are more likely to develop adverse outcomes following a primary TJR. Our findings may assist clinicians in better selecting elderly patients for surgery, and informing them about their individual level of risk.