The factors that influence women in choosing between first-trimester chorionic villi sampling and second-trimester amniocentesis for prenatal diagnosis were investigated. Five hundred twenty women of advanced maternal age who had previously undergone prenatal diagnosis by amniocentesis and were delivered of a normal infant were requested to complete a questionnaire concerning their attitudes toward amniocentesis and chorionic villi sampling. The majority of respondents indicated that the time at which chorionic villi sampling is performed (76%), the rapid availability of diagnostic results (72%), and the type of abortion procedure available (68%) would make them choose this method. In contrast, the factors that influenced women to choose amniocentesis included the known low risk of spontaneous abortion (76%) and confidence in the skill of the obstetrician who would perform the procedure (56%). When all factors were considered together, 68% of the respondents chose amniocentesis based on the known low risk of spontaneous abortion, whereas for those who chose chorionic villi sampling (32%), the major criterion was the fact that the procedure is performed in the first trimester. However, 87% of women who preferred amniocentesis indicated that if the risk of spontaneous abortion associated with chorionic villi sampling. These results indicate that for many women of advanced maternal age, the acceptability and the use of chorionic villi sampling will be dependent on the demonstration that the risk of fetal loss is low, approaching that of amniocentesis.