Valganciclovir to Treat HHV-8 Associated Multicentric Castleman's Disease

Inclusion Criteria: * Age 18 years * Negative pregnancy test (for female participants) * Diagnosis of MCD for over one year, with a history of at least one MCD recurrence annually * Evidence of infection with HHV-8 * A willingness to travel and reside temporarily in Seattle for completion of the study protocol. * For HIV-infected participants, a stable antiretroviral regimen for the past 6 months Exclusion Criteria: * Concurrent Kaposi sarcoma or non-hodgkin's lymphoma * A history or evidence of CMV disease * Hypersensitivity to ganciclovir or valganciclovir * Use of high-dose acyclovir (\>800 mg bid), valacyclovir (\>1000 mg qd) or famciclovir (\>1000 mg qd), ganciclovir, foscarnet, or cidofovir * Neutropenia (ANC \<1500) * Renal insufficiency with serum creatinine \> 1.5 mg/ml or CrCl \< 60 * AST or ALT \> 5 times upper limit of normal * Concurrent administration of medications which are often associated with severe neutropenia or thrombocytopenia (i.e., chemotherapy, etc) * Concurrent administration of probenecid or didanosine. * Inability to read and understand English