Surface marker and gene rearrangement data have supported various hypotheses about the origin of the malignant cell in Hodgkin's disease. Cytogenetic data about this disorder, however, are very scanty. To determine if any chromosomal abnormalities that could add further information to this controversial point are present, we studied tumor samples from 49 patients. Abnormal metaphases were obtained in 18 cases. The most common breakpoints were in 11q23, 14q32, 6q11–21, and 8q22–24. These are common breakpoints in lymphoma and raise the possibility that the malignant cell in Hodgkin's disease may be derived from a lymphocyte. The 11q23 breakpoint is also seen in t(4;11) and t(9;11), which is typical of a type of childhood B-cell acute lymphoblastic leukemia characterized by the presence of aberrant myeloid and monocytic markers. Myeloid and monocytic markers are common in Reed-Sternberg cells.