PURPOSE: The purpose of this study was to describe the sonographic findings of healing in torn common extensor tendon of elbow after prolotherapy and to evaluate the value of US in the course of management of lateral epicondylitis. MATERIALS AND METHODS: 12 common extensor tendons in eleven patients were examined by sonography before and after prolotherapy. On initial US examination, 11 tendons showed a partial tear and one tendon showed a full thickness but incomplete width tear. All patients were managed with prolotherapy several times(2 to 6 times). The time interval between the initial US and follow up US examination after treatment was from 4.5 to 6.5 months(mean ; 5.8 months). The findings of healing were evaluated with respect to the change of echogenicity(anechoic focus, hypoechoic focus), presence or absence of fibrillar pattern in the tendon on gray scale US, and focus of hypervascularity on color Doppler image. We used the visual analogue scale(VAS) of pain to assess the response to the treatment. RESULTS: All patients showed symptom improvement as the points drop on VAS in a range betwen 1.5 and 6.5(mean ; 4.5). In one tendon, a few echogenic lines were seen within the initially anechoic lesion(pattern I). In three tendons, most of the anechoic lesion(tear) was filled with fibrillar echogenicity except for a small focus of anechogenicity(pattern II). In two tendons, initial anechoic lesion in common extensor tendon was changed to same sized hypoechoic lesion with diffuse fibrillar pattern within the initial anechoic lesion (pattern III). In 6 tendons, initial anechoic lesion became smaller with diffuse fibrillar pattern were seen(pattern IV). Color Doppler examination was performed in 11 tendons after therapy and six of 11 tendons showed hypervascularity. CONCLUSION: Most important finding of healing in torn tendon is reappearance of fibrillar pattern in initial anechoic lesion(tear). The follow up sonography of the common extensor tendon in the course of treatment can be useful to evaluate the effects of the management.