Tumor blood flow is dependent on the structure and three-dimensional (3-D) architecture of the vascular network. The latter can be best studied by scanning electron microscopy of microvascular corrosion casts. However, literature reviews show that nearly all studies using this technique render comparisons of different tumors more difficult since they are mainly based on descriptive terms that might lead to misunderstandings. Qualitative comparisons of 13 experimental and 3 human primary tumors of different origin show a high degree of similarity in the vasculature. Quantitative analysis of these casts reveals similar ranges of parameters such as diameters, intervascular and interbranching distances. Diameters of vessels with capillary wall structure range from 6 micron m to 55 micron m in the human primary tumors (renal clear cell carcinoma, basalioma), and from 5 micron m to 80 micron m in xenografted tumors (sarcomas, colon carcinoma). Intervascular distances in the human primary tumors range from 2 micron m to 52 micron m, and from 11 micron m to 105 micron m in the xenografts. Interbranching distances range from 34 micron m to 258 micron m in the former, and from 11 micron m to 160 micron m in the latter. Both qualitative and quantitative analyses of tumor microvascular corrosion casts enable pathophysiological conclusions to be drawn and contribute to a better understanding of tumor vascularity.