An additional six cases of mycobacterial infection other than by Mycobacterium tuberculosis and involving synovial structures are reported. Follow-up is included on a previously reported case. Five of the patients in the present series had involvement of tendon sheaths of the hand, wrist, and forearm. The causative microorganism was Runyon Group III (Battey bacillus) in two and Mycobacterium avium in two others; one tendon-sheath infection was due to Mycobacterium kansasii. An elbow was infected with Mycobacterium kansasii and a prepatellar bursa, with Mycobacterium fortuitum. We believe surgical excision of involved synovial tissue to be very important; antibacterial treatment is of importance in selected cases.