Objectives To investigate the completeness of reporting of physical therapy interventions in randomized controlled trials before and after publication of the Template for Intervention Description and Replication (TIDieR) checklist (a reporting guideline for interventions). Design Meta-research. Methods We searched 6 journals for trials using physical therapy interventions that were published in 2000 and 2018. Two independent assessors scored the TIDieR checklist and extracted descriptive information, including Physiotherapy Evidence Database (PEDro) scale scores. We identified control or treatment interventions, exercise-based interventions, and area of physical therapy. We performed a descriptive analysis and defined a priori a 20% difference between studies published in 2000 and 2018 as meaningful. We assessed correlations between TIDieR and PEDro scale scores for all interventions. Results In total, 140 articles that met selection criteria evaluated 225 interventions (2000, n = 61; 2018, n = 164). Mean ± SD TIDieR score (2000, 7.52 ± 2.62; 2018, 8.26 ± 2.26) did not show a meaningful difference between years for all interventions (+5%), controls (+6%), treatment interventions (+6%), exercise-based interventions (+9%), or musculoskeletal (+4%) or neurological (+7%) physical therapy. For exercise interventions, number of sessions was reported more (+21%) in 2018 than in 2000. For musculoskeletal trials, 2 items were reported more completely in 2018 than in 2000 (materials, +29%; individual versus group, +22%) and 3 items were reported more completely in neurological trials (mode of delivery, +20%, [item 8.1] when +45%, and assessment of fidelity, +20%). The item “Who delivered the intervention?” was reported less completely (−23%) in 2018 than in 2000 in neurological trials. We found no correlation (r = 0.12) between PEDro scale score and TIDieR score. Conclusion There were few meaningful improvements in how physical therapy interventions were described after publication of the TIDieR reporting guideline. J Orthop Sports Phys Ther 2021;51(10):503–509. doi:10.2519/jospt.2021.10642