BACKGROUND: How changes in recommendations for the use of knee arthroscopy have influenced real-world practice remains unclear. We assessed temporal trends in knee arthroscopy volume, costs, and rates of progression to knee arthroplasty following arthroscopy in Ontario, Canada. METHODS: We used diagnostic codes from population-based administrative databases from Ontario, Canada, to identify patients who underwent knee arthroscopy from April 1, 2004 to March 31, 2019. We calculated arthroscopy volume, costs, and rates of progression to knee arthroplasty within 1, 2, and 5 years following arthroscopy. RESULTS: A total of 408,040 arthroscopy procedures were included. The number of procedures declined 8.9% from 24,070 in 2004/2005 to 21,930 in 2018/2019. The volume of arthroscopy for osteoarthritis declined by 77.9% between 2007/2008 and 2018/2019. For degenerative meniscus disorders, the volume increased by 57.6% between 2004/2005 and 2013/2014, and then declined by 34.6% between 2013/2014 and 2018/2019. Among patients with osteoarthritis, rates of progression to knee arthroplasty were 3.8%, 9.6%, and 16.0%, at 1, 2, and 5 years, respectively, compared with rates among patients with degenerative meniscal disorders, which were 1.6%, 4.1%, and 7.3% at 1, 2, and 5 years, respectively. Over this period, progression to knee arthroplasty rates declined across diagnosis groups. These trends remained after adjusting for patient, surgeon, and hospital characteristics. CONCLUSIONS: In Ontario, Canada, utilization of knee arthroscopy declined between 2004/2005 and 2018/2019, with a concomitant decline in the rates of progression to knee arthroplasty within 1 to 5 years. Among the possible interpretations, our data are consistent with the hypothesis that clinical practice evolved as evidence-based recommendations against the use of knee arthroscopy for degenerative diagnoses were promulgated. (Funded by the Toronto General and Western Hospital Foundation through the University Health Network–Schroeder Arthritis Institute.)