The prognosis for patients with mantle cell lymphoma (MCL) treated with conventional chemotherapy remains poor. Dose escalation and stem cell transplantation has been increasingly employed in an attempt to improve the outcome in these patients. However, due to the advanced age of many patients with MCL, high dose therapy and allogeneic stem cell transplantation is particularly hazardous. Reduced intensity allogeneic transplantation (RIT) may reduce the toxicity of allogeneic stem cell transplantation, facilitate allogeneic engraftment and graft versus lymphoma reactions. However, the results reported to date with this treatment modality have been based on small numbers of patients and provide conflicting results. We have therefore analysed the outcome of a large cohort of patients with MCL reported to the EBMT registry who have undergone RIT. A total of 144 patients (123 male) with a histological diagnosis of MCL were reported by 81 centres. The median age at transplant was 49 years (range 28–68 years) and the median time from diagnosis to transplant was 25 months (range 0.25–13.2 years). The patients had received a median of 2 (range 1–5) lines of prior chemotherapy and 60 (42%) had undergone a prior high dose procedure. At the time of RIT 100 patients had chemosensitive disease, 22 chemoresistant disease and 22 had untested relapse. Patients underwent conditioning with reduced intensity regimens prior to transplantation with allogeneic peripheral blood stem cells (122), bone marrow (20) or both (1). Fully matched sibling donors were used in 109 cases, matched unrelated donors in 21 and 9 patients received mismatched stem cells. 123 of 126 patients assessable for engraftment demonstrated sustained engraftment. With a median follow up of 9 months 84 patients remain alive and 60 have died (15 from progressive disease and 45 from non-relapse mortality). The transplant related mortality (TRM) was 12% at 100 days but by Kaplan-Mier analysis the TRM was 35% at 1 year and 50% at two years. In univariate analysis there was a non-significant trend to a higher TRM in patients with chemoresistant disease (p=0.067) and those with a prior transplant (p=0.062). Patient age and the number of lines of prior therapy had no impact on TRM. At two years following transplant 57% of patients had evidence of disease relapse or progression which was significantly worse in those with chemoresistant disease prior to transplant (p=0.02). The overall survival (OS) at 1 year and 2 years was 55% and 31% respectively and was worse for patients with chemoresistant disease. The progression free survival (PFS) at 1 and 2 year was 43% and 26% respectively. Only disease status at transplantation predicted for a worse PFS. Acute GVHD (grade II-IV) developed in 52 patients and chronic GVHD in 23 patients. Although the early transplant related toxicity is low there remains a significant TRM following RIT for MCL and consequently a low progression free survival. Patients with chemoresistant disease have a particularly poor outcome.