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The morphologic, phenotypic, molecular genetic, and clinical features of 34 cases of clear-cell immunoblastic lymphoma (IBLC) are described. Sixteen cases were of B-cell type (IBLC-B) and 18 cases were of T-cell type (IBLC-T). There were no significant differences in the morphologic characteristics of the neoplastic cells in the two types, although IBLC-B was less likely to be polymorphic than IBLC-T. Interfollicular proliferation, a higher mitotic rate, infiltration by eosinophils, and an increase in capillary-sized blood vessels were also features of IBLC-T, whereas necrosis and fibrosis were more extensive in IBLC-B. Patients with IBLC-B were predominantly female, whereas those with IBLC-T were predominantly male. The mean age was 62 years for those with IBLC-B and 46 years for those with IBLC-T. Patients with IBLC-B usually had lower-stage disease, but there was no significant difference in survival rate between those with IBLC-B and those with IBLC-T. Although most cases of IBLC have been considered to be of peripheral T-cell origin, the authors conclude that IBLC-B is more common than previously considered and that clear-cell morphologic characteristics are not a reliable indicator of T-cell type.