Chronic painful tendinopathy is a common cause for elite- and recreational athletes to stop or decrease the level of their sports activity. Recent research on innervation patterns, histopathology and possible pain mechanisms in tendons has led to an increased knowledge about the chronic painful tendon. Ultrasound (US) and colourDoppler (CD) examination showing localized high blood flow, inside and outside regions with structural tendon abnormalities, has been shown to be of importance for tendon pain. Immuno-histochemical analyses of biopsies have shown sensory and sympathetic nerves in close relation to the high blood flow outside the tendon. These findings have led to new ideas about development of new treatment methods for chronic painful tendinopathy. In study I, we evaluated the already in use, US-guided sclerosing polidocanol injection treatment of midportion Achilles tendinopathy, using two different concentrations of the substance. This study aimed to find out if there was a faster return to pain-free activity by using the concentration 10 mg/ml compared to the formerly used 5 mg/ml. There were no significant differences in the clinical results between the groups. In study II - Technical note, we aimed to develop a new one-stage surgical treatment method for patellar tendinopathy. This method was based on research concerning the innervation patterns and US and CD findings in patellar tendinopathy/ “jumper’s knee”. Technically we added ultrasound guidance to knee arthroscopy to identify and visualize the region of interest during a surgical shaving procedure. In study III, we tested the newly invented US and CD-guided arthroscopic shaving technique in a pilot study. The short-term clinical results were promising and the majority of the patients returned to pain-free activity after a short rehabilitation period. In study IV, we compared the US and CD-guided artrhroscopic shaving method with the already in use sclerosing polidocanol injection treatment in a randomized study. At short-term follow-up, the patients treated with US and CD-guided arthroscopic shaving had significantly less pain during rest and activity, were significantly more satisfied with the treatment, and had a faster return to sports, compared to the patients in the sclerosing injection group. There were no complications. In study V, at longer-term followup (endpoint 46 months) there was a significant decrease in pain during activity in both groups. There were no remaining significant differences in the pain levels during activity between the groups. The tendon structure had improved significantly in both groups. There was a significant decrease in the antero-posterior thickness of the proximal patellar tendon in patients treated with US and CD-guided arthroscopic shaving, but not in the sclerosing injection group. The CD flow had diminished significantly in both groups, and there was a correlation between low CD flow and high patient satisfaction in both groups, The CD flow decreased faster in the surgical group than in the injection group. In conclusion, this newly invented US and CD-guided arthroscopic shaving treatment, focusing on treatment outside the tendon, has shown good clinical results with pain relief and a fast return to sports activity, in patients with patellar tendinopathy.