Tumor angiogenesis has been related to tumor growth and an increased probability of metastatic spread. Previous studies have led to conflicting views regarding the prognostic significance of angiogenesis in squamous cell carcinoma of the head and neck. To evaluate the role of tumor angiogenesis in the biology of squamous cell carcinoma of the larynx, we quantified the microvascular network in 59 primary laryngeal carcinomas and looked for an association with outcome. Microvessels were stained immunohistochemically using antibodies for factor VIII-related antigen and the antibody JC70 (CD-31). In each case, microvessels were counted in three fields at x200 magnification, in areas of most intense neovascularization. We found a significantly higher number of microvessels in tumors showing deeper levels of invasion.