PURPOSE: This study aimed to investigate the effect of unsupervised isometric exercise compared to a wait-and-see approach on pain, disability, global improvement and pain-free grip strength in individuals with lateral elbow tendinopathy (LET). METHODS: Forty participants with unilateral LET of at least 6 weeks' duration were randomised to either wait-and-see (N=19) or a single supervised instruction session by a physiotherapist, followed by an 8-week unsupervised daily program of progressive isometric exercise (N=21). Primary outcomes were Patient-Rated Tennis Elbow Evaluation (PRTEE), global rating of change on a 6-point scale (GROC, dichotomised to success and no success) and pain-free grip strength at 8 weeks. Secondary outcomes were resting and worst pain on an 11-point numerical rating scale (NRS), and thermal and pressure pain thresholds as a measure of pain sensitivity. RESULTS: Thirty-nine (98%) participants completed 8-week measurements. The exercise group had lower PRTEE scores compared to wait-and-see at 8 weeks (standardised mean difference (SMD) -0.92, 95% CI -1.58 to -0.26). No group differences were found for success on GROC (29% exercise vs 26% wait-and-see (risk difference 2.3%, 95% CI -24.5 to 29.1)), or pain-free grip strength (SMD -0.33, 95% CI -0.97 to 0.30). No differences were observed for all secondary outcomes except for worst pain, which was moderately lower in the exercise group (SMD -0.80, 95% CI -1.45 to -0.14).Unsupervised isometric exercise was effective in improving pain and disability, but not perceived rating of change and pain-free grip strength when compared to wait-and-see at 8 weeks. With only one out of the three primary outcomes being significantly different following isometric exercises, it is doubtful if this form of exercise is efficacious as a sole treatment.