Spontaneous rupture of the spleen is a rare complication of hematological malignancies, occurring most commonly in patients with acute leukemia, but it has been documented in chronic leukemias and also in lymphomas. We report two patients with histologically and immunohistochemically confirmed mantle cell lymphoma (MCL) who experienced a spontaneous splenic rupture. An 80-year-old woman and a 51-year-old man had a blastoid variant of MCL and responded poorly to conventional treatment. Both patients recovered after splenectomy. The woman died of progressive lymphoma 2 months later. An allogeneic bone marrow transplantation was performed in the man with a good initial result, but an aggressive relapse was seen only 6 months later and he died of progressive lymphoma. In view of our data, we suggest special caution when MCL is complicated by rapid progression and severe splenomegaly. Although it is a rare phenomenon, the risk of splenic rupture should be kept in mind.