PURPOSE: To evaluate the ultrasonographic findings of lateral epicondylitis and their relationship with clinical outcome. MATERIALS AND METHODS: The findings of ultrasonographic examinations of eighteen elbow joints in 15 patients [M:F=5:10 ; age:38-65(mean, 47.6) years] with lateral epicondylitis were reviewed. Two patients underwent surgery, two were not treated, and the remaining 11 were treated conservatively. Symptomatic improvement was noted 1 week after conservative treatment in two cases, at 2 weeks in five cases, at 3 weeks in three cases, and at 5 weeks in one case. With patients in the 90 degree flexed elbow position and in a supinated wrist, we examined the extensor carpi radialis brevis (ECRB) tendon around the lateral epicondyle using ultrasound equipment with a 7-11-MHz linear transducer. The findings were assessed in terms of swelling of the tendon, changes in its echotexture, the presence of calcification or cystic degeneration, loss of the hypoechoic band between the tendon and bony cortex of the lateral epicondyle, cortical irregularity of the lateral epicondyle, and fluid collection around the tendon. Any relationships between each ultrasonographic finding and the treatment interval after which symptomatic improvement was noted were evaluated. RESULTS: In the 18 joints, change was observed in the echotexture of all ECRB tendons. This included homogeneous hypoechogenicity in two cases, heterogeneous hypoechogenicity in 13, and heterogeneous mixed echogenicity in three. Other ultrasonographic findings were swelling of the tendon in ten cases, loss of the hypoechoic band in 14, cortical irregularity in five, calcification in four, cystic degeneration in nine, and fluid collection around the tendon in four. In patients treated conservatively, there was no statistically significant difference between each ultrasonographic finding and the treament interval after which symptomatic improvement was noted. CONCLUSION: Ultrasonography can be used to assess changes in the ECRB tendon and lateral epicondyle occurring in lateral epicondylitis, but fails to provide information on the rapidity of symptomatic improvement.