Although molecular remissions have been frequently observed and associated with low likelihood of relapse in some lymphoid tumours, they are seldom reported in mantle cell lymphoma (MCL). We performed PCR analysis of a MCL patient with central nervous system (CNS) relapse occurring 76 months after autologous transplantation. Molecular follow-up showed constant absence of PCR-detectable disease, even after the onset of relapse. These data indicate that isolated CNS relapse may occur even after several years of continuous remission and cannot be excluded based on a persistent pattern of molecular remission. However, the prolonged remission duration observed in this patient suggests that achieving PCR-negativity may also be of benefit for MCL patients.