To determine the acceptability of chorionic villi sampling (CVS) to women eligible for prenatal diagnosis, we undertook a survey to identify aspects of this new procedure that made it more or less preferable than amniocentesis. All women greater than or equal to 35 years scheduled for amniocentesis were asked to read some detailed descriptive material about amniocentesis and CVS, to rate the importance of the specific differences between procedures, and to indicate which procedure they would prefer, first considering each difference between them independently and then considering all the factors jointly. In the absence of precise estimates of CVS-associated risk at the time of the survey, almost equal proportions preferred amniocentesis and CVS (50.2 and 45.1%, respectively). Risk information was the most important factor to women preferring amniocentesis; the timing of the test or nature of the termination procedure was most important to those preferring CVS. In the hypothetical case where CVS was stipulated to have the same attributable risk as amniocentesis, 82% of respondents would prefer it. However, if the spontaneous abortion rate following CVS was stipulated to be 5% more than the amniocentesis risk, preferences reversed and only 22% would still prefer it. Thus, the data suggest that the ultimate acceptability of the new procedure for women over 35 years seeking prenatal diagnosis will depend on the risk associated with it and underscore the importance of ongoing trials aimed at establishing this risk.