To compare the feasibility of blinding and the perceived risk of unblinding in trials evaluating pharmacologic (PT) and nonpharmacologic treatments (NPT) of hip or knee osteoarthritis. Two independent reviewers assessed the feasibility of blinding patients, care providers, and outcome assessors, the perceived risk of unblinding, and whether blinding was reported in 110 reports of randomized controlled trials (RCTs) evaluating PT and NPT in patients with hip or knee osteoarthritis. Blinding was considered to be possible less often in NPT trials than in PT trials for patients (42 vs. 96%; P <.001), care providers (12 vs. 96%; P <.001), and outcome assessors (34 vs. 98%; P <.001). When blinding was judged feasible, the perceived risk of unblinding was more often considered moderate or important in NPT than PT trials for patients (35 vs. 14%, P=.02) and outcome assessors (44 vs. 10%, P=.0004). When blinding was judged feasible, it was reported less often in NPT reports than in PT reports for patients (46 vs. 98%, P <.001), care providers (43 vs. 83%, P=.03), and outcome assessors (72 vs. 98%, P=.0006). Blinding appears to be more difficult to achieve and unblinding may occur more often in NPT than PT trials.