The chronic painful tendon is well known to be difficult to treat, and the source of pain has not been scientifically clarified. For chronic painful conditions in the Achilles-, patellar-, and ECRB tendons there is no treatment of choice, but a huge variety of proposed treatment regimens. There is sparse scientific evidence for most of the conservative and surgical treatments proposed and used. Recent research, using ultrasonography (US) together with colour Doppler (CD), and immunohistochemical analyses of biopsies, has demonstrated a vasculo-neural (SP- and CGRP-nerves) ingrowth in the area with structural tendon changes. Also, tendon pain was temporarily cured by US- and CD-guided injections of a local anaesthetic targeting the neovessels outside the tendon. A specially designed treatment were US- and CD-guided injections of the sclerosing agent Polidocanol (primarily acting on the intima layer in the vascular wall), aiming to destroy the neovessels and accompanying nerves, has in pilot studies cured the tendon pain in the majority of patients with chronic painful Achilles and patellar tendinosis. Follow-ups ( > 2 years) showed remaining good clinical results, a significantly decreased tendon thickness, no remaining neovessels, and ultrasonographically a more normal tendon structure. The importance of using Polidocanol, was verified in a randomized double-blind study.