OBJECTIVE: To study efficacy and safety of corticosteroid injections for trigger finger (flexor tenosynovitis) in adults in general practice. METHODS: Adult patients presenting with trigger finger were recruited by 21 participating general practitioners. In this randomised placebo controlled double-blinded trial, patients were injected locally with one or two injections of 1 ml triamcinolonacetonide (TCA) or 0.9% NaCl. Outcomes regarding immediate treatment response, severity of symptoms, functional disability, patient satisfaction and side effects were measured 1 week after intervention and during the 12 months thereafter. RESULTS: A total of 50 patients were included. Short-term outcomes for the TCA and NaCl group, respectively, were: proportion of patients with satisfactory immediate treatment response 16/25 and 5/25 (p<0.001), patients with reduction in the frequency of triggering 13/24 and 6/22 (p = 0.053), mean difference in severity of pain 4.2 and 0.9 (p<0.001), patients perceiving improvement 22/25 and 9/25 (p<0.001) and difference in Arthritis Impact Measurement Scale 2 (AIMS-2) score 4.02 and 0.06 (p = 0.001). Long-term effects could only be assessed by analysing the cohort of participants who received TCA (as allocated treatment or escape treatment), due to a high proportion of non-responders in the NaCl group. The short-term beneficial effects were maintained during the follow-up phase of 12 months. Patients were satisfied with corticosteroid injection therapy and there were only a few minor side effects. CONCLUSIONS: Local injection with TCA is effective and safe for treating trigger finger as compared to placebo injection. The effects of steroid injections last up to 12 months.