Summary:The authors performed a retrospective clinicopathologic review of lymphoid tumors of the orbit and ocular adnexa. In addition, we used an immunohistologic marker for proliferating cell nuclear antigen (PCNA), an intranuclear protein with greatest expression in actively proliferating (dividing) cells, to determine whether levels of PCNA can be correlated with the presence or future development of systemic lymphoma. To the authors' knowledge, the present study represents the first in which PCNA indices, i.e., the number of cells that showed diffuse intranuclear staining for PCNA averaged per 10 high power field (HPF), were correlated with systemic disease in orbital and ocular adnexal lymphomas. The percentage of B- and T-cells in the tumor infiltrate was also determined. Followup data showed that two patients with eyelid involvement had preexisting systemic lymphoma, whereas another with bilateral lacrimal gland disease later developed systemic lymphoma. Followup times ranged from 24 to 42 months (mean 39.7 months). The mean PCNA level in three patients with systemic disease was 13.3 and in the six patients with no systemic disease was 33.8. These results suggest that PCNA alone cannot be used as a marker for the presence of, or development into, systemic lymphoma.