Studies in the pre-biologics era described elevated risk of infection in patients with rheumatoid arthritis (RA). Recently biologics have been popularized and glucocorticoids used still now in RA patients, which can lead to various infections. Incidence rates of infection in RA patients are reported to be higher than that in the general population. Several factors such as higher age, comorbidities including chronic lung disease and diabetes mellitus, and glucocorticoids are known to increase risk of serious infection. Significant correlation between methotrexate and infection is not established. Whether biologics, especially inhibitors of tumor necrosis factor alpha, increase the risk for infection is still controversial even with randomized control studies and the meta-analyses; however, time-dependent decrease of the risk was revealed. Our three-year analysis of RA patients for infections requiring hospitalization included 5441 patient-years (PY) in total and detected an incidence rate of 3.4/100 PY, of which the risk factors were higher age (70 years of age or older), male sex, progressed stage of arthritis, functional disorders, and use of glucocorticoids or biologics. Such risk factors should be kept in mind for therapeutic decisions in individual patients with RA.