During a 30-month period, 51 needle-arthroscopic procedures using a small diameter (1.9 mm) flexible fiberoptic arthroscope were performed to obtain synovial tissue from knee joints. This procedure was performed in an outpatient setting using only a local anesthetic. Twenty-eight procedures were conducted involving 23 rheumatoid arthritis patients and 1 osteoarthritis patient as part of research protocols. In addition, arthroscopy and synovial biopsy were performed on 23 patients to obtain tissue for diagnostic purposes. Large samples of synovial tissue (over 10 g) were easily obtained in most patients. No complications were observed., The easy accessibility to large quantities of synovial tissue provided by needle arthroscopy should enable investigators to better define the pathogenic mechanisms operative in early rheumatoid arthritis. In addition, this technique will afford opportunities for determining the influence of current treatments as well as experimental treatments on molecular events in the synovium of patients. We conclude that outpatient needle arthroscopy using a small fiberoptic arthroscope can be used safely by rheumatologists trained in arthroscopy to obtain synovial biopsies for research and diagnostic purposes. © 1995 by Williams and Wilkins.