Abstract In classical Hodgkin lymphoma, circulating clonotypic malignant cells express CD20, which potentially explains the observed activity of rituximab. This multicenter phase 2 study investigated the combination of rituximab-ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine) for stage II-IV untreated classical Hodgkin lymphoma. A goal was to assess the behavior of circulating clonotypic B cells clinically. Of 49 evaluable patients, 69% had stage IIB-IV disease; 8% had CD20+ Hodgkin and Reed-Sternberg cells. Rituximab-ABVD was generally well tolerated. Delivered relative dose intensity was 94% for AVD and 79% for bleomycin. After 6 cycles, 81% of patients were in complete remission. Only 8% received radiation therapy. The actuarial 3-year event-free and overall survival rates were 83% and 98%, respectively. EBV copy number in plasma fell dramatically during cycle 1 in patients with EBV+ tumors. Persistence of detectable circulating clonotypic B cells was associated with a greater relapse frequency (P < .05). Rituximab-ABVD and clonotypic B cells warrant additional study in classical Hodgkin lymphoma. This trial was registered at www.clinicaltrials.gov as NCT00369681.