Background. This placebo-controlled, double-blind study evaluated the short-term effects of betamethasone valerate (BMV) 2.25mg medicated plaster in patients with chronic lateral elbow tendinopathy (LET). Methods. Adult outpatients with LET and on-movement pain intensity ≥50 mm at a 0-100mm visual analogue scale (VAS) were randomised to receive BMV (N=101) or placebo (N=98), 12 hours/day for 4 weeks. Pain decrease from baseline to Day 28 was the primary endpoint. Other endpoints were: patient-rated tennis elbow evaluation (PRTEE), use of rescue paracetamol, tolerability at the application site. Results. Decrease in mean pain VAS from baseline to Day 28 was significantly higher with BMV vs. placebo: the difference between groups (intent-to-treat) was-8.57 mm (95% CI:-16.19 to-0.95 mm; p=0.028). Higher pain decreases in the BMV group over placebo were reported weekly during each control visit and daily in patients' measurements on diaries. Treatment with BMV also led to higher decreases vs. placebo in PRTEE total, pain and functional disability score. Use of paracetamol was minimal. BMV plaster was well tolerated for general and local adverse events. Conclusions. BMV 2.25mg plaster was superior to placebo and well tolerated in patients with painful chronic LET.