Total hip and knee arthroplasty (THA and TKA) are among the most reliable medical interventions, providing pain relief and long survivorship in the vast majority of patients. Nonetheless, some patients are at higher risk of complications and sub-optimal outcomes following total joint arthroplasty (TJA). Obesity has been proposed in some literature as a risk factor for poorer outcomes and increased complications following TJA. Given the high prevalence of patients living with obesity in Canada, and the continuing rise in the prevalence of overweight and obesity, it is important to understand the relationship between obesity and TJA outcomes. Thus, the aim of this study was to evaluate the short-, medium-, and long-term outcomes of TJA in patients with different body mass index (BMI) classifications. Data was retrieved from a prospectively collected and maintained institutional database. All patients undergoing TJA since September 1998, and who had at least 1 year follow-up, were included. Patients were classified based on BMI category. Baseline and post-operative (1 year, 2 years, 3 years, 5 years, 7 years, and 10 years) Oxford scores were collected. Revision surgery and mortality were collected from provincial data and linked with patient records. Analysis of Variance (ANOVA) was performed to compare continuous outcomes across groups, while Chi-Square was used to compare categorical data. A total of 10,851 patients were included (4216 THA, 6635 TKA). Sixty-one percent (6601/10851) were female, and 39% (4246/10851) were male. There was no significant difference between patients with and without obesity in terms of change from baseline in Oxford score at 1, 2, 3, 5, 7, or 10 years post-operatively. Reoperation rates ranged from 3.1% to 4.4% across BMI groups, with no significant differences between groups. Overall mortality was 26.8% in non-obese patients, and 23.3% in obese patients (p < 0.01). The findings were similar when TKA and THA patients were analyzed separately. Patients with obesity have comparable gains from baseline following TJA at short-, medium-, and long-term. Reoperation and mortality rates are also similar in the long term, with a statistically significant lower mortality rate among patients with obesity. Obesity is associated with a range of health conditions, and can lead to more difficult TJA operations, which may be associated with increased risk of infection and less precise implant positioning. However, based on this large institutional database, functional gains, revision rates, and mortality rates are similar between obese and non-obese patients.