Constitutive activity of nuclear transcription factor kappaB (NF-kappaB) is observed in many pathological types of lymphoma that are associated with a poor clinical course. This suggests that NF-kappaB and pathways involving NF-kappaB are possible targets for successfully treating lymphoma. We examined 28 lymph nodes from 28 patients in whom follicular lymphoma was diagnosed from 1996 to 2006 at our institution, which were formalin-fixed and paraffin-embedded. The specimens were stained with an antibody that could recognize activated NF-kappaB and p65 to determine whether they were positive or negative for NF-kappaB activation. The clinical courses of the 28 patients were then correlated with the results of the NF-kappaB staining. The 10 men and 18 women had a mean age of 57.3 years (range, 25-87 years). By follicular lymphoma grade, 10 patients had grade 1, 16 had grade 2, and 2 had grade 3a. Ten patients died due to lymphoma. NF-kappaB was positive in 6 of the 28 cases. Analysis of the positive and negative staining groups while taking into account the clinical course, sex, age, grade of follicular lymphoma, prognostic index, CD10, CD23, Bcl-2, karyotype t(14;18), and survival showed that no significant differences. Six of the 28 lymph nodes (21.4%) exhibited consistent NF-kappaB activity. Three of the eleven cases that transformed to aggressive lymphoma were positive for activated NF-kappaB. Further research to clarify the significance of constitutive NF-kappaB activity in follicular lymphoma is therefore warranted.