Tumor angiogenesis is required for tumor growth and metastasis. A statistically significant correlation has been demonstrated between prognosis and the microvessel density (a measure of tumor angiogenesis) of solid tumors, particularly of the breast and prostate, and lymphoid neoplasms. The aim of this study was to establish whether a correlation exists between vascular density and the malignant category of Non-Hodgkin's Lymphoma (NHL) defined by two classification systems (Kiel and Working Formulation). We also tested whether florid follicular hyperplasia (FFH) and follicular lymphomas (FL) behave as new vessel stimulating conditions. Eighty-nine NHL lymph node biopsies were reviewed and categorized according to the Kiel Classification and Working Formulation. Twelve FL were also selected and compared to 12 FFH biopsies. Vessels were highlighted by immunostaining with anti-Factor VIII antibody and quantified both by counting higher vascular density fields and by estimating the proportional vascular area. The results showed a statistically significant difference between low and high grade NHL, when classified in either the Working Formulation (p=0.0015) or the Kiel Classification (p=0.002). No differences were found in vessel counts between Working formulation intermediate and high grade lymphomas. Vascular density is similar when FFH and FL interfollicular areas are compared.