Castleman disease (CD) is a nonclonal lymphoproliferative disorder that can affect single lymph node stations or, alternatively, can be generalized. Interleukin 6 (IL6) plays a pivotal role in the pathophysiology of CD. Human herpesvirus 8 (HHV8), which encodes a viral homolog of IL6, is the driving force in HIV-positive patients. The role of HHV8 in HIV-negative CD is controversial. Historically, the prognosis of patients with generalized or multicentric CD has been thought to be poor. However, CD responds extremely well to monoclonal antibodies directed at the IL6 receptor or IL6 itself, and in general, the long-term outcome of HIV-negative CD is excellent. Important strides forward have also been made in the management of HIV-positive CD.