The clinical features, morphology and immunophenotype of 20 cases of B non Hodgkin's lymphoma (B-NHL) with chromosome abnormalities involving 11q13-14 were studied, to determine if this abnormality was closely associated with a specific sub-type of B-NHL. A t(11;14)(q13;q32) was found in 11 cases of intermediately differentiated lymphocytic lymphoma (IDLL). A breakpoint in the major translocation cluster of the BCL-1 locus was found in six of these cases. These patients were male with lymphomatous involvement of the bone marrow, marked splenomegaly and frequently had mucosa associated lymphoid tissue involvement. One patient with IDLL had a t(8;11)(p21;q13) and a rearranged BCL-1 locus, suggesting that this may be a variant of t(11;14)(q13;q32). Diagnoses of IDLL, chronic lymphocytic leukaemia, lymphoplasmacytic lymphoma and monocytoid B cell lymphoma were made in all but one of the remaining cases. These cases had either a translocation involving 11q13-14 and various partner chromosomes or an 11q13 deletion. This study demonstrates that 11q abnormalities occur mainly in a group of low-grade B-NHL of non follicle centre cell lineage.