Castleman disease (CD) is a rare, heterogeneous lymphoproliferative disorder for which no standard of care currently exists. Evidence that the pathophysiology of CD is fueled by excessive interleukin-6 (IL-6) has led to considerable interest in therapeutic targeting of this cytokine. Siltuximab, a chimeric monoclonal antibody to IL-6, has thus emerged as a promising treatment option in a disease lacking efficacious therapy. Here, we review the findings of recent studies evaluating single-agent siltuximab treatment in CD, including the first-ever randomized clinical trial in this disease. Although much more work is needed to establish a standardized treatment approach, siltuximab appears to be a safe and effective treatment for patients with newly diagnosed and previously treated CD.