Assessment of relationship between density, perimeter and endothelial surface (“endothelial area”, EA) of vascular spaces (VS) using “ImageJ” analysis and morphological characteristics of adenocarcinoma. Introduction: Colorectal adenocarcinoma invasion involves complex reaction of tumor cells and stroma, whereas angiogenesis is essential for metastatic potential. Material and Methods: 70 resected specimens were reviewed. For each adenocarcinoma histological grade, pathological stage, lymphatic, venous and perineural invasion, growth pattern, metastases in lymph nodes and liver were determined. For visualization of vascular endothelial cells immunohistochemical staining CD31 antibody was used. From each tumor nine fields were photographed: three from invasive front, three from VS highest density and three selected randomly. Computer analysis of images was done using program “ImageJ”. For analysis of EA (EA representing surface area of CD31 positive endothelial cells) program recalculated them as percentage of tested fields (% area). VS density was shown as number VS per 1mm2, while perimeter of VS was shown in Results of all parameters were compared with all above described morphological characteristics. Results: There was no significant correlation between density and perimeter of VS and any of histopathological findings. EA from randomly chosen fields (minimum 0,69%, maximum 10,11%, p=0,016) correlates with the presence of venous invasion. There was no significant correlation between EA from the invasive front and areas of the highest density and any of the histopathological findings. Conclusion: Assessment of vascular endothelial surface area is only vascular parameter which positively correlates with prognostic parameters that could indicate worse outcome.