IMPORTANCE: There is limited evidence supporting use of physical therapy for hip osteoarthritis. OBJECTIVE: To determine efficacy of physical therapy on pain and physical function in patients with hip osteoarthritis. DESIGN, SETTING, AND PARTICIPANTS: Randomized, placebo-controlled, participant- and assessor-blinded trial involving 102 community volunteers with hip pain levels of 40 or higher on a visual analog scale of 100 mm (range, 0-100 mm; 100 indicates worst pain possible) and hip osteoarthritis confirmed by radiograph. Forty-nine patients in the active group and 53 in the sham group underwent 12 weeks of intervention and 24 weeks of follow-up (May 2010-February 2013) INTERVENTIONS: Participants attended 10 treatment sessions over 12 weeks. Active treatment included education and advice, manual therapy, home exercise, and gait aid if appropriate. Sham treatment included inactive ultrasound and inert gel. For 24 weeks after treatment, the active group continued unsupervised home exercise while the sham group self-applied gel 3 times weekly. MAIN OUTCOMES AND MEASURES: Primary outcomes were average pain (0 mm, no pain; 100 mm, worst pain possible) and physical function (Western Ontario and McMaster Universities Osteoarthritis Index, 0 no difficulty to 68 extreme difficulty) at week 13. Secondary outcomes were these measures at week 36 and impairments, physical performance, global change, psychological status, and quality of life at weeks 13 and 36. RESULTS: Ninety-six patients (94%) completed week 13 measurements and 83 (81%) completed week 36 measurements. The between-group differences for improvements in pain were not significant. For the active group, the baseline mean (SD) visual analog scale score was 58.8 mm (13.3) and the week-13 score was 40.1 mm (24.6); for the sham group, the baseline score was 58.0 mm (11.6) and the week-13 score was 35.2 mm (21.4). The mean difference was 6.9 mm favoring sham treatment (95% CI, -3.9 to 17.7). The function scores were not significantly different between groups. The baseline mean (SD) physical function score for the active group was 32.3 (9.2) and the week-13 score was 27.5 (12.9) units, whereas the baseline score for the sham treatment group was 32.4 (8.4) units and the week-13 score was 26.4 (11.3) units, for a mean difference of 1.4 units favoring sham (95% CI, -3.8 to 6.5) at week 13. There were no between-group differences in secondary outcomes (except greater week-13 improvement in the balance step test in the active group). Nineteen of 46 patients (41%) in the active group reported 26 mild adverse effects and 7 of 49 (14%) in the sham group reported 9 mild adverse events (P = .003). CONCLUSIONS AND RELEVANCE: Among adults with painful hip osteoarthritis, physical therapy did not result in greater improvement in pain or function compared with sham treatment, raising questions about its value for these patients. TRIAL REGISTRATION: anzctr.org.au Identifier: ACTRN12610000439044.