The pathologic findings of 118 patients aged 70 years or older with non-Hodgkin's lymphoma (NHL) are reported. These patients formed 27.2% of 433 consecutive cases of NHL seen in a single institution over a 5-year period. Thirty-one of 433 NHL cases were histologically not classified, whereas the remaining 402 could be classified according to the International Working Formulation (WF) of NHL for clinical usage. Immunophenotypic analyses were carried out in 112 NHL cases; of this group 28 were NHL in elderly patients. Of the 95 elderly NHL that could be classified in the histologic categories of the WF 28 cases were in the low-grade, 41 in the intermediate-grade, and 26 in the high-grade categories. Eighty-one cases had diffuse histologic types and 14 had follicular/nodular histologic types. Thirty-five cases were of the G (diffuse large cell) + H (large cell, immunoblastic) categories. No significant differences in the prevalence of the different subtypes were observed among patients younger or older than 70 years. Immunohistologically, most NHL cases in the elderly expressed B-cell phenotype. Sixty-two NHL in the elderly were extranodal at presentation. The results of this study indicate that elderly patients form a relevant proportion of patients developing NHL and thereby present a very difficult management problem. The pathologic features of NHL in the elderly does not differ significantly from those of their younger counterparts, although an increase in diffuse versus follicular histologic patterns, and in extranodal versus nodal disease was observed with advancing age.