Effective targeting of workplace upper extremity musculoskeletal disorder (MSD) prevention strategies requires the identification of demographic groups most at risk. Workers' compensation data provides an effective means of surveillance of MSDs at the population level. The primary purpose of this study was to identify the effects of age and sex on rates of tendon injuries of the wrist and hand, carpal tunnel syndrome (CTS), epicondylitis, and soft tissue shoulder injuries in Ontario, Canada between 2000-2019 using workers' compensation data from the Association of Workers Compensation Boards of Canada (AWCBC). Age and sex specific rates of lost-time injury claims from the four identified injury categories as well as "non-specific" upper extremity MSDs which did not fit into the four categories were calculated by standardizing injury claim totals with "at-risk" population estimates from the Canada Labour Force Survey. A multiple regression analysis was used to analyze the effects of age and sex on rates of specific injury claims. Statistically significant age and sex effects were identified for rates of claims from tendon injuries of the wrist and hand, CTS, and shoulder injuries, while only age effects were significant for epicondylitis. Between 2000-2019, rates of claims from the four injury categories studied and the magnitude of the age and sex effects declined substantially over time. Detailed surveillance of workplace ergonomic hazards in Ontario workplaces is needed to determine what is causing rates of upper extremity claims to decline.