The clinical course and therapy of mantle cell lymphoma (MCL) are heterogeneous and often unsatisfactory. Prognostic factors are needed to stratify the patients. Microvessel density (MVD) has prognostic significance in some malignancies. There is little information about the vasculature of MCL, although some antiangiogenic drugs are in use. We studied MVD using systematic uniform random sampling and unbiased counting frames in immunohistochemical reactions with anti-CD34 antibody in pre-therapeutic extramedullary MCL samples of 177 patients. We analyzed the relationship of MVD to overall survival (OS) and progression-free survival (PFS), as well as to proliferative activity (Ki-67), mantle cell lymphoma prognostic index (MIPI), morphological variant, pattern of growth, and localization. MVD varied widely: range 54.6-503.6 vessels/mm(2), median 158.2 vessels/mm(2). Higher MVD was associated with bone marrow infiltration at the time of diagnosis (P = 0.001). High MVD was associated with significantly worse OS (P = 0.04) only in patients treated with non-intensive (conventional) therapy. MVD correlated positively with MIPI scores but not with the proliferation, morphological variant, growth pattern, or localization. Univariate analysis identified a prognostic influence of morphological variant, MIPI, and proliferative activity on OS and PFS and a prognostic influence of bone marrow infiltration at the time of diagnosis on PFS. Multivariate analysis showed prognostic influence of MIPI and proliferative activity on OS and PFS only. In conclusion, this is the first clinicopathological study of MVD of MCL with long-term follow-up showing negative prognostic trends of high MVD in MCL and positive correlation of MVD and MIPI.