The aim of the research was to reveal vascular endothelial growth factor (VEGF) immunolocalization in endometrioma, cysts and endometrial tissues. The study group (group1) included 15 patients laparoscopically operated on for endometrioma and the control group (group 2) included 13 patients prepared for diagnostic laparoscopy for primary infertility. Biopsies from endometrioma cyst capsules, disease-free peritoneum and pipette biopsies from the endometrium were taken from group 1. Biopsies from parietal peritoneum and endometrium were taken from group 2. Results showed VEGF immunoreactivity of peritoneal biopsies of group 1 was more intense than that of the control biopsies. A positive correlation was seen between the diameter of cyst capsules and VEGF labeling intensity and as the size of cyst enlarged, the appearance of non-homogeneous distribution of VEGF immunolocalization became more frequent. We conclude that the variation of VEGF immunolocalization in endometrioma cysts may be attributed to other possible angiogenic molecules in the pathogenesis and may cause unexpected responses to anti-angiogenic therapies. (C) 2008 Elsevier GmbH. All rights reserved.