Objectives/AimsObesity and its increasing prevalence are global public health concerns. Following joint replacement, there is evidence to support that obese patients are more likely to suffer complications. We examined 10-year trends in BMI of the primary total hip and total knee replacement cohorts in our institution to discern whether the BMI of these patients has changed over time.MethodsWe examined BMI data of patients who underwent primary hip and knee arthroplasty from our institutional database from January 1, 2010 to December 31, 2019 (n=12,169). We analysed trends in BMI over this period with respect to (i) surgical procedure, (ii) gender, and (iii) age categories.ResultsThe overall number of surgical procedures increased over the study period which meant more obese patients underwent surgery over time. Average BMI did not change significantly over time; however, there was a statistically significant increase in BMI in females aged < 45 in both arthroplasty groups.ConclusionThe average BMI of patients undergoing primary hip and knee arthroplasty in our high-volume tertiary orthopaedic centre has remained relatively unchanged over the past 10 years; however, our local service is caring for a greater number of overweight/obese patients due to the increase in overall volume. This will have significant implications on health care expenditure and infrastructure going forward which further emphasises the importance of ongoing national obesity prevention strategies. The increase in BMI seen in females aged < 45 may mark an impending era of obese younger patients with end-stage osteoarthritis.Supplementary informationThe online version contains supplementary material available at 10.1007/s11845-022-03092-w.