In the hematologic malignant diseases, specific cytogenetic abnormalities correlate with clinical, morphologic, and immunophenotypic features. Although relatively little is known regarding the karyotypic pattern of Hodgkin's disease, it is clear that the involvement of specific chromosomes in numerical and structural abnormalities is nonrandom. Hyperdiploidy is a characteristic feature of Hodgkin's disease and is observed in 70 per cent of tumors that have an abnormal karyotype. A gain of chromosomes 1, 2, 5, 12, and 21 is a recurring numerical abnormality; structural rearrangements involving chromosome 1 are frequently observed. Perhaps as a result of the relatively small number of cases that have been analyzed, recurring structural abnormalities have not yet been identified; it has also not been possible to determine whether the various histologic subtypes of Hodgkin's disease are characterized by unique abnormalities. The prognostic significance of cytogenetic abnormalities in Hodgkin's disease is unclear; however, preliminary results suggest that the karyotype may have prognostic importance in this disease. The correlation of the cytogenetic pattern with the clinical and morphologic features will be essential in evaluating the clinical and biologic significance of chromosomal abnormalities in Hodgkin's disease.