Background: Adult T-cell leukemia-lymphoma (ATLL) is a rapidly progressive systemic illness with the causative agent, the human T-cell lymphotropic virus type -1. It is endemic in the Japan, Africa, Brazil and recently, North East of Iran, particulary the region of Mashhad. The role of angiogenesis is appreciated in development and prognosis of many malignancies. To examine a possible association between tumor angiogenesis and ethiopathogenic and prognostic role of it in ATL patients this study was performed.Methods: This study included 20 ATL patients examined between 2004 and 2006. Microvessel density (MVD) was identified immunohistochemically, using monoclonal anti-CD34 antibody. The MVD of tumoral tissue was defined by counting the number of microvesseles in three hot spots, and the mean values indicated the Microvessel density (MVD). As the control group, normal tissues were examined with the same procedure.Results: There was statistically significant increase in MVD of tumoral tissue of ATL patients (Mean =17.78) compared to normal tissues (M = 3.54) [p=0.000].Conclusion: Intratumoral Microvessel density quantification in histologic specimens of ATL patients reflects the biologic malignant potential and may be valuable in stratifying patients in planning appropriate adjuvant and anti-angiogenesis therapy.