Objective of the Review: To discuss the significance and possibility of non–invasive diagnosis of small forms of endometriosis, consider the features, advantages and disadvantages of transvaginal ultrasound (TV–ultrasound) and magnetic resonance imaging (MRI). Key points. Endometriosis in women of reproductive age can cause both pain and infertility. Currently there is no single and generally accepted classification of endometriosis. Laparoscopy with histological examination is no longer the “gold standard” for diagnosing this disease, which leads to an urgent need to find alternative non–surgical methods. The only presently proven possibility of non–invasive verification of endometriosis is the use of radiation diagnostic methods. TV ultrasound is a first–line imaging modality, but it has limitations in terms of field of view and dependency on the skill and experience of the operator. MRI, used as a method for verifying endometriosis foci, has some limitations in visualizing small endometriotic implants and adhesions, but at the same time, it allows characterizing lesions, studying extraperitoneal localizations and the contents of formations located in the pelvic cavity. Conclusion. The lack of a single generally accepted classification creates difficulties both in the diagnosis of endometriosis and in the selection of the correct treatment for the condition. For the diagnosis of deep endometriotic foci, the specificity and sensitivity are quite high for TV–ultrasound (87–94% and 79–92%), and medium for MRI (77 and 94%), however, for verification of superficial foci, neither MRI nor TV–ultrasound at this moment have superior diagnostic accuracy compared to laparoscopy. Both methods are the most promising, but require improving the quality of diagnostics, which largely depends on the experience of specialists and improving the power of the instruments used. Proper staging of the disease, in turn, will greatly help in choosing the tactics of infertility treatment. Keywords: external genital endometriosis, MRI, ultrasound, "small" forms of endometriosis, non–invasive diagnostics of endometriosis.