The clinicopathological and biological significance of Hodgkin's disease and non-Hodgkin's lymphoma, which are infrequently encountered in women of childbearing age, remains to be clarified. We recently reviewed 4 cases of non-Hodgkin's lymphoma of the T/natural killer (T/NK)-cell phenotype, all of which were associated with pregnancy and characterized by the expression of the cytotoxic granule-associated proteins T-cell intracellular antigen-1 and/or granzyme B. The 4 cases selected had presented between November 1993 and May 1999. The criteria for selection were that the onset of clinical manifestations occurred during pregnancy or within 6 months after delivery. The patients comprised 1 patient with p80/anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL), 1 with p80/ALK-negative ALCL, and 2 with peripheral T/NK-cell lymphomas of unspecified type. The diseases followed aggressive clinical courses: 3 patients died within 6.5 months after diagnosis, and only 1 was still alive with the disease 17 months after diagnosis. The diseases appeared to progress rapidly after delivery. Maternal immunity and hormonal changes during pregnancy may be closely related to the biological behavior of these unusual tumors. This study is, to the best of our knowledge, the first to address pregnancy-associated cytotoxic lymphoma.