Prenatal testing in the form of amniocentesis or chorionic villus sampling is commonly recommended for women 35 years of age or older as well as those found by screening to be at high risk of having an infant with a chromosomal abnormality such as Down syndrome. When these guidelines were developed in the 1970s, age 35 was the approximate time at which amniocentesis was cost-beneficial. The authors report the findings from a cost-utility analysis of amniocentesis and chorionic villus sampling versus no invasive testing. Data were taken from randomized trials, case registries, and a utility assessment of 534 pregnant women ranging in age from 16 to 47 years. The decision model that was used addresses the decision to carry out diagnostic testing based on age-adjusted risk or revised risk estimates after screening. At age 35 years, the incremental cost-utility ratio for amniocentesis was approximately $12,600 per quality-adjusted life years (QALY). The cost-utility ratio remained below $15,000 per QALY regardless of maternal age. This figure did not change despite wide variations in probability estimates. Less than $50,000 per QALY gained is within the generally accepted range for routine healthcare interventions. The results also were independent of the risk of a Down syndrome birth. For any particular woman, the cost-utility ratio depended on her preferences for reassurance about the chromosomal status of her fetus and, to a lesser degree, for miscarriage. When a probabilistic sensitivity analysis was carried out by running 50,000 simulations and changing all variables in the model except for patient utilities, the cost utility of testing was less than $30,000 per QALY gained in more than 99.98% of the simulations. This cost-utility analysis does not support the current practice of limiting amniocentesis and chorionic villus sampling to women aged 35 and older and those who are at high risk of bearing a chromosomally abnormal fetus. The investigators believe that prenatal diagnostic testing should be offered to all pregnant women. It is most important to take individual preferences into account when making decisions about prenatal testing.