OBJECTIVE To determine the adequacy of genetic risk assessment among primary care providers and to evaluate the efficacy of genetic counseling before "routine" genetic amniocentesis. METHODS A retrospective cohort study was undertaken. Charts of 275 consecutive patients referred for genetic counseling and amniocentesis on the basis of advanced maternal age (AMA) were compared with charts of 103 consecutive patients referred for an abnormal maternal serum alpha-fetoprotein (MSAFP) finding. Pedigree information obtained during counseling of these patients was compared with the family histories charted by the referring physician. RESULTS In 35.6% of pedigrees evaluated, a significant genetic risk was discovered during genetic consultation that had not been noted by the referring physician. Furthermore, 9.8% of AMA patients and 10.7% of patients with abnormal MSAFP results underwent additional genetic testing or screening on the basis of genetic counseling. Additional genetic testing of 0.8% of amniotic fluid specimens was done on the basis of the genetic risk assessment elicited during counseling. Although a significant difference in increased genetic risk was observed between the AMA and abnormal MSAFP groups (AMA 30.8% positive, MSAFP 48.5% positive; relative risk 0.81, confidence limit 0.70 to 0.93), no significant difference was observed between the two groups with regard to patient interventions (relative risk 0.97, confidence limit 0.79 to 1.21) or amniotic fluid testing (p = 0.57, not significant). CONCLUSIONS The data support the importance of genetic counseling before amniocentesis. Furthermore, the findings support the relevancy and usefulness of genetic counseling in more accurately ascertaining genetic risk and in maximizing the benefits of genetic evaluation of patients seemingly at low risk for other genetic diseases.