Fifteen cases of low-grade B-cell lymphoma involving unusual extranodal sites have been studied in comparison to cases reported or observed arising in typical mucosa-associated lymphoid tissues. In every case, histopathologic features conformed to those characteristic for lymphomas of mucosa-associated lymphoid tissues, including the production of lymphoepithelial complexes. Immunoglobulin light chain restriction was demonstrated by immunocytochemistry in 14 cases. Sites of involvement included the breast (6), skin (5), kidney (1), prostate (1), gallbladder (1), and uterine cervix (1). In three cases there was simultaneous or previous lymphoma of mucosa-associated lymphoid tissues identified in a more common mucosal site. It is concluded that the unifying concept of lymphomas of mucosa-associated lymphoid tissues applies to extranodal organs less commonly associated with mucosa-associated lymphoid tissues, as well as to those mucosal organ sites described in earlier series.