Ultrasound-guided puncture is a simple and easy to perform procedure. It would seem to be a good idea to suggest simple puncture as a first intention in cases of an image of ovarian cyst. In theory, the advantages are obvious: a puncture is performed, the liquid is analyzed and an appropriate treatment is administered. Coelio-surgery could surely be avoided in cases of functional cysts and perhaps in some non-malignant ovarian cysts. In fact, it must be remembered that a cancer of the ovary in its early stages may have the appearance of a banal cyst, and that puncture does not allow pathological examination. Cytological examination is insufficient to totally rule out malignancy or to allow detailed histological diagnosis. There is, therefore, a risk of leaving in place the pocket of a cyst which may be organic and which may recur or even develop. For these reasons, ultrasound-guided puncture can be undertaken only in pre-selected patients and in the context of a specific protocol: 1) The ultrasound image of the cyst must be liquid, anechoic, unilocular (or bilocular with a fin wall), with no vegetation, the serum level of CA 125 must be low; 2) it the puncture liquid is oily, tarry or viscous, a celioscopy must be carried out as soon as possible, only a yellow-colored liquid can justify waiting; 3) the analysis of the cyst fluid is not always determinant, and the cytology findings are conclusive only if positive. A high 17 beta-estradiol level suggests a functional cyst.(ABSTRACT TRUNCATED AT 250 WORDS)