Sclerosing polidocanol injections targeting the area with neovessels (vascularity) have been demonstrated to give promising clinical results in patients with chronic painful Achilles and patellar tendinosis. Recently, we demonstrated vascularity in the extensor origin in patients with chronic painful tennis elbow, but not in controls with pain-free elbows. In this pilot study, 11 patients (four men and seven women, mean age 46 years) with the diagnosis of tennis elbow in altogether 13 elbows, were included. All patients had a long duration of pain symptoms (mean 23 months), and ultrasonography (US) + colour Doppler (CD) examination showed structural tendon changes with hypo-echoic areas, and a vascularity, corresponding to the painful area in the extensor origin. All patients were treated with US- and CD-guided injections of the sclerosing substance polidocanol, targeting the area with vascularity. At 8-month follow-up after treatment, there was a good clinical result in 11/13 elbows. Extensor origin pain during wrist loading activities (recorded on a VAS-scale) was significantly reduced (mean VAS from 75 to 34; P < 0.003), and maximal grip strength was significantly increased (from 29 to 40 kg; P < 0.025). Our findings indicate that one treatment with sclerosing polidocanol injections, targeting the area with vascularity in the extensor origin, has a potential to reduce the tendon pain and increase grip strength, in patients with chronic painful tennis elbow.