Four cases of rheumatoid arthritis with a total of 12 undisplaced stress fractures of the lower extremities are described. Pain, swelling and disability arising from these fractures were initially mistaken for rheumatoid synovitis. Three patients had osteoporosis, and one had osteomalacia. A high index of suspicion is necessary in the diagnosis of these fractures. Radiographs and, if necessary, bone scans are indicated in rheumatoid patients presenting with spontaneous pain in the lower extremities in association with tenderness localized over the bone rather than the joint, particularly in the absence of other signs of rheumatoid activity.