The aim of our study was to qualitatively and quantitatively investigate the capillary architecture on lectin Ulex Europaeus agglutinin I-stained histological section in prostatic intra-epithelial neoplasia. The capillaries appeared as small, short or elongated vessels with either a smooth or undulated external contour and either virtual or visible lumen, sometimes with a clearly identifiable endothelial nucleus/i. In the benign prostatic hyperplasia and prostatic intra-epithelial neoplasia categories, the capillaries appeared located in close contact with (i.e. touching) or in proximity to the basement membrane of ducts and acini. In the invasive adenocarcinoma category, on the contrary, the capillaries in general appeared interspersed within the tumour stroma and septa. Our quantitative studies of the capillary architecture showed that, going from benign prostatic hyperplasia through prostatic intra-epithelial neoplasia up to invasive adenocarcinoma, an increasing proportion of capillaries becomes shorter, with open lumen and undulated external contour and with a greater number of endothelial cells. The highest proportion of touching capillaries was seen in benign prostatic hyperplasia, while the lowest was in invasive adenocarcinoma, being intermediate in prostatic intra-epithelial neoplasia. When the prostatic intra-epithelial neoplasia samples were divided into low-grade and high-grade, the feature values in the low-grade approached those in benign prostatic hyperplasia, whereas in the high-grade they were close to invasive adenocarcinoma. Half of the benign prostatic hyperplasia samples were taken from total prostatectomies because of the preoperative diagnosis of prostatic adenocarcinoma. The feature values in this subcategory were close to those of prostatic intra-epithelial neoplasia of low grade.