Sonography represents one of the best methods of clinical investigation which might give information about the preimplantation prognosis by evaluation of the following parameters:--morphological parameters (with bidimensional sonography): thickness and structure of the endometrium;--functional parameters (with doppler): evaluation of uterine vascularisation. The prognostic value of the morphological parameters appears to be controversial:--thickness of endometrium: a linear correlation between endometrial thickness and implantationsuccess may not exist. However no pregnancy occurs without a minimum threshold value of 6 to 8 mm endometrial thickness;--structure of the endometrium: concerning the role of the endometrial structure, controversial studies are available. According to some authors, endometrial hyperechogenicity is incompatible with a pregnancy. However hypoechogenic endometrium with 5 well delimited layers is an excellent prognostic factor. The coloured pulsed Doppler allows a functional assessment of the uterus and represents a technical progress in sonography investigations since the early nineties. The evaluation of uterine vascularisation can take place at different levels of the uterine vessels.--The pregnancy rate is inversely proportional to the uterine pulsatility index (PI). There is a consensus concerning a threshold value of PI. With values above 3, the pregnancy rate drops significantly.--The presence of a protodiastolic notch and the absence of end diastolic blood flow have bad prognosis. The presence or not of a sub-endometrialen vascular flow may be the most important prognostic parameter. No pregnancy may occur by absence of these flows. The sonography gives not only important morphological informations about endometrium but also allows a study of the uterine vascularisation by coloured doppler. This allows a real assessment of endometrial potentials for implantation. Optimal conditions of implantation could be:--endometrium > 7 mm,--hypoechogenic endometrium with 5 well delimited layers,--uterine PI < 3,--presence of sub-endometrial vascular flow.