Mantle cell lymphomas are characterized by a male predominance with a range between 55 and 65 years (sex ratio M/F of 6.5). When the sex ratio of patients having mantle cell lymphoma was compared to that of each of the subtypes of non-Hodgkin's lymphomas, it was significantly higher in all cases except Burkitt's and lymphoblastic T-cell lymphomas. These observations suggest a possible relation between the chromosome X and mantle cell lymphomas which has to be explored.