ObjectivesTo compare the clinical effectiveness of (1) physiotherapist-led exercise versus an exercise leaflet, and (2) ultrasound-guided subacromial corticosteroid injection versus unguided injection for pain and function in subacromial pain (formerly impingement) syndrome (SAPS).MethodsThis was a single-blind 2×2 factorial randomised trial. Adults with SAPS were randomised equally to one of four treatment groups: (1) ultrasound-guided corticosteroid injection and physiotherapist-led exercise, (2) ultrasound-guided corticosteroid injection and an exercise leaflet, (3) unguided corticosteroid injection and physiotherapist-led exercise and (4) unguided corticosteroid injection and an exercise leaflet. The primary outcome was the Shoulder Pain and Disability Index (SPADI), collected at 6 weeks, 6 and 12 months and compared at 6 weeks for the injection interventions and 6 months for the exercise interventions by intention to treat.ResultsWe recruited 256 participants (64 treatment per group). Response rates for the primary outcome were 94% at 6 weeks, 88% at 6 months and 80% at 12 months. Greater improvement in total SPADI score was seen with physiotherapist-led exercise than with the exercise leaflet at 6 months (adjusted mean difference −8.23; 95% CI −14.14 to -2.32). There were no significant differences between the injection groups at 6 weeks (−2.04; −7.29 to 3.22), 6 months (−2.36; −8.16 to 3.44) or 12 months (1.59; −5.54 to 8.72).ConclusionsIn patients with SAPS, physiotherapist-led exercise leads to greater improvements in pain and function than an exercise leaflet. Ultrasound guidance confers no additional benefit over unguided corticosteroid injection.Trial registration numberISRCTN42399123.