Cystic rheumatoid arthritis: description of a nonerosive form. In a study of patients with rheumatoid arthritis (RA), 9% (n = 70) were found to have a cystic form. At radiologic examination of these patients with cystic RA, the first abnormality seen consisted of periarticular intraosseous cysts without erosions. The cysts were distributed symmetrically, most often located at the proximal side of the joints and predominantly around the proximal interphalangeal, metacarpophalangeal, and wrist joints of the hands and the first interphalangeal and metatarsophalangeal joints of the feet. Computed tomographic scans showed the peripheral intraosseous location of the cysts. Magnetic resonance images showed that the cysts may contain fluid, inflamed synovia, or both. Cysts can be an important feature in the diagnosis of RA and a supplement to the criteria of the American Rheumatism Association. Osteoporosis, joint-space narrowing, and joint destruction occurred less frequently in patients with cystic RA than in patients with classic RA. Of the patients with cystic RA, 54% were male, and 50% were seronegative. This study is a supplement to and an enlargement on earlier descriptions of cyst predominance in RA. 