Objectives: It has previously been reported that lateral epicondylitis may be diagnosed with colour Doppler by detecting hyperaemia inside the common extensor origin (CEO). In this study, we report on the association between ultrasound (US) Doppler findings and the short-term response of US-guided corticosteroid injection in patients with LE. <br> Design: Case-only, blinded intervention study.<br> Setting: Secondary care at government hospital.<br> Patients: 62 patients with LE verified by colour Doppler.<br> Intervention: One US-guided corticosteroid injection was given into the CEO.<br> Main Outcome Measurements: Patients were evaluated at baseline before the injection and at two weeks follow-up. Outcome was changes in pain score and US parameters (resistive index (RI) and amount of colour within the CEO). Prognosticators for outcome were: Use of computer mouse, symptom duration, elbow strain, RI, colour fraction, Likert pain score, rest pain, pain at activity, age, height, weight, disease in dominant versus nondominant arm. <br> Results: All but one patient experienced improvement of general elbow pain perception at two weeks follow-up. In parallel, Doppler US showed significant reduction in colour fraction (baseline 0.14 ± 0.10, at follow-up 0.02 ± 0.02, p<0.0001). All but five patients showed a decrease in colour fraction – 74 % decreased to 0. No clinical or US parameter could distinguish responders from non-responders. <br> Conclusion: Corticosteroid injection has marked short term effect on pain and Doppler parameters. We interpret the reduction in hyperaemia mediated by an anti-inflammatory drug as evidence of an inflammatory component in LE.