We studied demographic socioeconomic and clinical characteristics of 38 patients with fibrositis (fibromyalgia) that occurred in association with rheumatoid arthritis (RAFIB) and 242 patients with rheumatoid arthritis (RA) alone. Fewer RAFIB patients were married (57.1%), and most (97.4%) were women. No statistically significant differences in income, medical expenditures or other demographic variables were identified. All measures of function, pain, disease activity and psychological status were more abnormal in RAFIB patients. The clinical characteristics that best differentiated RAFIB and RA patients were pain, depression, anxiety and erythrocyte sedimentation rate, in logistic and stepwise regression models. Evaluation of disease severity markers, including radiographic erosions and frequency of total joint replacement, suggested that disease severity in RAFIB and RA is similar.