Whereas the hematologic, immunophenotypic, and molecular characteristics of splenic lymphoma with villous lymphocytes (SLVL) have been well documented, the histologic features of the spleen and lymph nodes remain uncharacterized. We have reviewed the histopathology of the spleen in 37 cases of SLVL and of involved splenic hilar lymph nodes in 6 cases. Tissue immunophenotyping was performed in 24 cases, 6 of which had frozen tissue available, and the results were compared with the membrane immunophenotype of the circulating villous lymphocytes and cells extracted from spleen and lymph nodes. In the spleen, SLVL is characterized by involvement of the white pulp follicles, which may be surrounded or replaced by the lymphoma cells. In the red pulp, the cells form small nodules and infiltrate diffusely with sinusoidal invasion. The cytologic appearance of the neoplastic cells varies from a resemblance to small mantle-zone--like lymphocytes to that of marginal-zone cells and there are scattered blast forms. In involved lymph nodes, the infiltrate again centers on the follicles that are usually replaced, but occasionally show preservation of follicle centers; sinuses are often preserved. The tissue immunophenotype is similar to that of marginal-zone B cells. Membrane immunophenotyping may give different results in some cases and may vary depending on the compartment from which the cells are obtained. SLVL in the peripheral blood is a histologically homogeneous entity identical to the condition previously characterised by histopathologists as splenic marginal-zone lymphoma.