Objective: This study aims to investigate the impact of digital image compression on manual and semiautomatic quantification of angiogenesis in ovarian epithelial neoplasms (including benign, borderline, and malignant specimens). Design: We examined 405 digital images (obtained from a previously validated computer-assisted analysis system), which were equally divided into 5 groups: images captured in Tagged Image File Format (TIFF), low and high compression Joint Photographic Experts Group (JPEG) formats, and low and high compression JPEG images converted from the TIFF files. Measurements: Microvessel density counts and CD34 endothelial areas manually and semiautomatically determined from TIFF images were compared with those from the other 4 groups. Results: Mostly, the correlations between TIFF and JPEG images were very high (intraclass correlation coefficients >0.8), especially for low compression JPEG images obtained by capture, regardless of the variable considered. The only exception consisted in the use of high compression JPEG files for semiautomatic microvessel density counts, which resulted in intraclass correlation coefficients of <0.7. Nonetheless, even then, interconversion between TIFF and JPEG values could be successfully achieved using prediction models established by linear regression. Conclusion: Image compression does not seem to significantly compromise the accuracy of angiogenesis quantitation in the ovarian epithelial tumors, although low compression JPEG images should always be preferred over high compression ones. © 2011 by Lippincott Williams & Wilkins.2019195Green, H.S.N., Heterologous transplantation of mammalian tumours. The transfer of human tumours to alien species (1941) J Exp Med, 73, pp. 461-468Folkman, J., Tumor angiogenesis: Therapeutic implications (1971) N Engl J Med, 285, pp. 1182-1186Folkman, J., Anti-angiogenesis: New concept for therapy of solid tumors (1972) Ann Surg, 175, pp. 409-416Folkman, J., What is the evidence that tumors are angiogenesis dependent? (1990) Journal of the National Cancer Institute, 82 (1), pp. 4-6Folkman, J., Angiogenesis in cancer, vascular, rheumatoid and other disease (1995) Nat Med, 1, pp. 27-31Krebel, R.S., Tumour angiogenesis: Past, present and the near future (2000) Carcinogenesis, 21, pp. 505-515Sharma, R.A., Harris, A.L., Dalgleish, A.G., Angiogenesis as a biomarker and target in cancer chemoprevention (2001) Lancet Oncol, 2, pp. 726-731Folkman, J., Shing, Y., Angiogenesis (1992) J Biol Chem, 267, pp. 10931-10934Risau, W., Differentiation of endothelium (1995) FASEB J, 9, pp. 926-933Roland, D., Ferder, M., Kothuru, R., Faierman, T., Strauch, B., Effects of pulsed magnetic energy on a microsurgically transferred vessel (2000) Plastic and Reconstructive Surgery, 105 (4), pp. 1371-1374Schoell, W.M.J., Pieber, D., Reich, O., Lahousen, M., Janicek, M., Guecer, F., Winter, R., Tumor angiogenesis as a prognostic factor in ovarian carcinoma: Quantification of endothelial immunoreactivity by image analysis (1997) Cancer, 80 (12), pp. 2257-2262. , DOI 10.1002/(SICI)1097-0142(19971215)80:12<2257::AID-CNCR6>3.0. CO;2-RHasan, J., Byers, R., Jayson, G.C., Intra-tumoural microvessel density in human solid tumours (2002) British Journal of Cancer, 86 (10), pp. 1566-1577. , DOI 10.1038/sj.bjc.6600315López, C.L., Effects of image compression on automatic count of immunohistochemically stained nuclei in digital images (2008) J Am Med Inform Assoc, 15, pp. 794-798Tengowski, M.W., Image Compression in Morphometry Studies Requiring 21 CFR Part 11 Compliance: Procedure Is Key with TIFFs and Various JPEG Compression Strengths (2004) Toxicologic Pathology, 32 (2), pp. 258-263. , DOI 10.1080/01926230490274399Landis, J.R., Koch, G.G., The measurement of observer agreement for categorical data (1977) Biometrics, 33 (1), pp. 159-174Montgomery, D.C., Peck, E.A., (1982) Introduction to Linear Regression Analysis, , New York: John Wiley and Sons Inc