Over the past decade we have used a decision analytic model to counsel 840 patients (468 women, 381 men, 432 couples) about amniocentesis for prenatal diagnosis. The model explicitly considers the possibilities of miscarriage (both after amniocentesis and spontaneously), an affected child (as a function of maternal age), and various diagnostic errors. Prospective parents are shown the model after routine counseling is used to explain the options and potential outcomes. Using the lottery technique (in which they are asked to choose between therapeutic abortion and carrying a pregnancy to term without the benefit of amniocentesis, where the likelihood of an affected child is varied in a structured sequence), prospective parents expressed their attitudes on a utility scale, where zero corresponds to an unaffected child and where 100 corresponds to an affected child. On that scale, the mean assessed disutility of therapeutic abortion was 33.7 +/- 32.6 (35.8 +/- 32.1 among women, 30.9 +/- 32.9 among men). The decision model encourages couples to confront their attitudes toward specific reproductive outcomes, to clarify their values and to incorporate them, along with their current risks, into a logical decision about prenatal diagnosis.