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Objectives: The purpose of this study is to assess the prevalence and titer of rheumatoid factor (RF) in Korean health screening subjects and consecutive subjects with hepatitis B surface antigen (HBsAg) and to examine the factors influencing RF positivity. Methods: This study was performed in 37,660 patients (23,269 men, 14,391 women) without arthralgia, who participated in a health checkup program in 2009. Results: Approximately 3.7% of health screening subjects (3.3% of males and 4.4% of females) were positive for RF. Among subjects with HBsAg ( n = 1,494) and antibody for hepatitis C virus (HCV) ( n = 132), 11.8 and 10.6% were RF positive, respectively. There was a significant difference in the RF-positive rate between males and females. The RF-positive rate had a significant linear-by-linear association with aging, but there was no significant relationship between RF positivity and aging among subjects with HBsAg or anti-HCV antibody. Presence of HBsAg and anti-HCV antibody, positive C-reactive protein (CRP), and female sex were factors strongly associated with RF positivity. Conclusions: The rate of RF positivity in health screening adults and subjects with HBsAg in Korea can be estimated to be 3.7 and 11.8%, respectively. Clinicians should consider hepatitis B or C virus infection status, CRP positivity, and sex when interpreting RF-positive results. [ABSTRACT FROM AUTHOR]