Intermediate lymphocytic lymphoma has been operationally included among low-grade lymphomas, but few clinical data appeared to support definitely such an inclusion. The clinicopathologic features of 13 out of 14 cases of intermediate lymphocytic lymphoma either encompassing diffuse or mantle-zone pattern variants (ILL or MZL, respectively), diagnosed by conventional histology according to established criteria, are reported. Frozen section immunophenotypic analysis was also performed in 10 cases and enzyme studies were done in five. The 14 cases formed 6.9% of 203 non-Hodgkin's lymphomas (NHL) histologically diagnosed over a 2-year period. Among the 13 cases studied, there were nine males (five with ILL and four with MZL) and four females (one with ILL and three with MZL). Median age was 59 years. Splenomegaly (46%), high stage diseases (100%), involvement of bone marrow (92%) and peripheral blood (38%), and diffusion to and/or involvement of extranodal sites (38%), all were common findings at presentation. The 34 low-grade NHL of the total series classified according to the Working Formulation did not significantly differ from the ILL/MZL group in terms of frequency of involvement of bone marrow (69%) and peripheral blood (56%) as well as diffusion to and/or involvement of extranodal sites (26%). In ILL/MZL, therapy modalities were not uniform and the short follow-up time precluded firm conclusions on prognosis. Immunohistology demonstrated that ILL/MZL diagnosed by adequate morphologic criteria is a fairly homogeneous entity, also sharing most of its consistent immunological features with low-grade NHL. Thus, ILL/MZL is a relatively frequent and consistently recognizable clinical and pathological entity that may deserve a distinct place among NHL according to the Working Formulation. Proper clinical studies are needed to establish on a firmer basis the prognosis and optimal treatment of ILL/MZL.