Amniocentesis, and other prenatal genetic tests, have become a well-established feature of modern prenatal care. But these tests place a considerable decision-making burden on the expectant mothers to whom they are offered: the genetic issues involved are complex and the appropriate course of action sometimes ambiguous. Genetic counseling aims to help pregnant clients make an informed decision about prenatal genetic tests. But the clientele of prenatal genetic counseling has changed significantly in the years since the practice was established. Clients were once a self-selected group of women well-informed about the genetic services being offered. In contrast, clients now include an increasing number of women, particularly ethnic minority women, who had no prior knowledge of genetic testing, but were found to be at risk of birth defects after routine screening. Little is known about how well genetic counseling serves the needs of this new clientele. This paper investigates the possibility that miscommunication between genetic counselors and their Mexican-origin clients contributed to the higher rates of amniocentesis refusal. We interviewed 156 pregnant Mexican-origin women who screened positive on a blood test routinely offered in California to detect birth defects. We also observed the genetics consultations of a sub-sample of the women. We identified five common sources of miscommunication: (1) Medical jargon; (2) The non-directive nature of counseling; (3) The inhibitions of counselors stemming from misplaced cultural sensitivity; (4) Problems of translation; (5) Problems of trust. We found that many Mexican-origin women are skeptical of genetic testing and do not easily surrender their own lay theories about the causes of their condition. In order to dislodge the misunderstandings of their clients, counselors must give clients the opportunity to air their own views, however contrary to those of genetics professionals these may be.