The purpose of this study was to evaluate and classify sonographically the joint damage of the elbow in patients with rheumatoid arthritis. Standardized sonography of the elbow joint was performed in patients with rheumatoid arthritis between 1998 and 2002; from 2000 onwards in a controlled and prospective study. A grading of the joint damage was developed, evaluated and compared with the radiographic standard reference films of the Larsen classification. A total of 320 consecutive patients were included in this study; 250 elbows of 125 patients (93 women/32 men) were examined in a prospective way. Mean age was 62.5 years and mean disease duration was 11.9 years. The sonographically visible changes could be divided into six stages. In 24% of the patients graded Larsen 0, sonography detected definite abnormalities classified as stages 1 to 3. Sonography is a valuable tool to assess and classify elbow joint alteration in rheumatoid arthritis. Particularly in early stages of joint affection, ultrasound (US) is superior to X-ray in detecting soft tissue changes and minor erosions.