In small cell lymphomas, central nervous system (CNS) involvement has been considered to be very rare. Mantle cell lymphoma (MCL) is a distinct subtype of non-Hodgkin's lymphomas consisting of small or intermediate lymphatic B-cells. It has a poorer prognosis than the other small cell lymphomas. Only a few MCL patients with CNS involvement have been reported in the literature to date. We analyzed retrospectively the incidence, clinical characteristics, and outcome of CNS involvement in 94 patients with confirmed MCL treated at one center from 1980 to 1997. Four of the 94 patients (4%) developed CNS lymphoma during the median follow-up of 51 months. The diagnosis was based on clinical, cytological and radiological findings. CNS involvement appeared at 4.6, 56, 66, or 86 months from the diagnosis of MCL. All patients had neurological symptoms and a leukemic disease; two cases were seen with a blastoid morphology. Malignant lymphatic cells were detected in spinal fluid in all cases and parenchymal infiltrations in brain in two. All patients were treated with intrathecal chemotherapy, without response. Survival time after diagnosis of CNS lymphoma ranged from 18 to 55 days. At diagnosis, no adverse prognostic factors predictive of CNS lymphoma were found. CNS involvement was associated with a progressive leukemic disease as a late event or a blastoid transformation. The prognosis of MCL patients with CNS involvement is poor.