Recent progress in the management of rheumatoid arthritis (RA) is turning attention toward comorbidities, such as diabetes. The objectives of this review are to clarify the links between RA and diabetes and to assess potential effects of disease-modifying antirheumatic drugs (DMARDs) on diabetes. The increased insulin resistance seen in RA is closely linked to the systemic inflammation induced by certain proinflammatory cytokines such as tumor necrosis factor α (TNFα) and interleukin-6. The prevalence of type 2 diabetes is increased in patients with RA. Furthermore, certain DMARDs including hydroxychloroquine, methotrexate, TNFα antagonist, and interleukin-1β antagonists seem to improve the markers of glucose metabolism. In contrast, glucocorticoids tend to adversely affect glycemic control, particularly when taken chronically. Consequently, a crucial yet insufficiently applied rule is that cardiovascular risk factors must be sought and treated routinely, particularly as the choice of the DMARD may affect glucose metabolism.