The anti-interleukin-6 (IL-6) chimeric monoclonal antibody siltuximab is the first drug to be approved for the treatment of multicentric Castleman's disease (MCD) in the US and European union (EU), having gained approval under the FDA priority review program in the US and from an accelerated assessment and recommendation by the Committee for Medicinal Products for Human Use (CHMP) in the EU. Development of the drug is continuing in smoldering multiple myeloma. This article summarizes the milestones in the development of siltuximab leading to this first approval for MCD.