Local injections of the sclerosing substance Polidocanol has been demonstrated to give good clinical results in a pilot study on patients with chronic Achilles tendinopathy. In this study, 20 consecutive patients (9 men and 11 women, mean age 50 years) with chronic painful mid-portion Achilles tendinopathy were randomised to injection treatment with either Polidocanol (5 mg/ml) (group A) or Lidocaine hydro-chloride (5 mg/ml) + Adrenaline (5 microg/ml) (group B). Both substances have a local anaesthetic effect, but Polidocanol also has a sclerosing effect. The patients and the treating physician were blinded to the substance injected. The short-term effects were evaluated after a maximum of two treatments, 3-6 weeks apart. Before treatment, all patients had structural tendon changes and neo-vascularisation demonstrated with US and colour doppler. Under US and colour doppler-guidance, the injections targeted the area of neo-vascularisation just outside the ventral part of the tendon. For evaluation, the patients recorded the severity of Achilles tendon pain during tendon loading activity, before and after treatment, on a VAS. Patient's satisfaction with treatment was also assessed. At follow-up (mean 3 months) after a maximum of two treatments, 5/10 patients in group A were satisfied with the treatment and had a significantly reduced level of tendon pain (p < 0.005). In group B, no patient was satisfied with treatment. In the pain-free tendons, but not in the painful tendons, neo-vascularisation was absent after treatment. After completion of the study, treatment with Polidocanol injections (Cross-over in group B and additional treatments in group A) resulted in 10/10 and 9/10 satisfied patients in group A and B, respectively. In summary, injections with the sclerosing substance Polidocanol have the potential to reduce tendon pain during activity in patients with chronic painful mid-portion Achilles tendinopathy.