A systemic, malignant disorder of immunoblasts has been reported to occur as a late transition phase of immunoblastic lymphadenopathy in an older population. With a background of polyclonal gammopathy, drug sensitivity, lupus erythematosus or rheumatoid arthritis, there may develop a progressive "cloning out" of monomorphous immunoblasts to form immunoblastic sarcoma. Recently, a 17-year-old, postpartum girl without these bizarre hypersensitivity phenomena developed a rapidly fatal, systemically malignant process with severe clinical complications. No historical incitent was identified. The pregnancy had been uneventful and birth had produced a thriving, viable infant. This case may represent the youngest patient with primary, malignant immunoblastic disease occurring in the absence of a "hypersensitivity" state. A brief discussion of the clinical situation, management, and autopsy findings, is presented. Basic morphologic criteria for proper differentiation of malignant immunoblastic problems, lymphoma, and Hodgkin's disease are discussed.