OBJECTIVES: Cigarette smoking may influence rheumatoid arthritis (RA) disease incidence and may have direct biological effects on the lungs and systemically. This study sought to determine if cigarette smoking is associated with RA disease severity. METHODS: Clinical evaluations of patients seen in the University of Iowa rheumatology and orthopaedic ambulatory clinics were conducted. A letter of interest was mailed to 1701 patients who were first assigned an ICD-9-CM diagnostic code for RA in one of these clinics. A total of 857 patients expressed interest and were offered a clinical examination and 395 were evaluated over an 18 month period. Of these, 336 satisfied examiner criteria for prevalent RA and were included in the analysis. The disease characteristics and arthritis care utilisation of these patients seemed representative of prevalent cases in the general community. RA disease severity was assessed by radiographic bone erosions (graded as either present/ absent and using the Larsen system), rheumatoid factor seropositivity, and presence of subcutaneous rheumatoid nodules. RESULTS: Pack years of cigarette smoking was significantly associated with rheumatoid factor seropositivity (p = 0.0001), radiographic erosions (p = 0.024), and nodules (p = 0.051). After adjustment for potential confounders, smokers with > or = 25 pack years were 3.1 times more likely to be rheumatoid factor positive (95% CI 1.7, 5.6) and 2.4 times more likely to show radiographic erosions (95% CI 1.2, 4.5) than never smokers. Less severe radiographic disease seemed to be more strongly associated with cigarette smoking than more severe disease. CONCLUSION: Cigarette smoking may adversely influence the severity of RA in a potentially dose dependent fashion.