Rapid and safe prenatal diagnosis has become the standard of care in high-risk pregnancy. The safety and reliability of prenatal diagnosis by mid-trimester amniocentesis and first-trimester chorionic villus sampling (CVS) are reviewed, and accepted medical indications for referral are defined for both procedures. Techniques for evaluating the fetus for abnormality including amniocentesis, CVS, ultrasound, percutaneous umbilical blood sampling, fetal biopsy, amniotic fluid alpha-fetoprotein analysis, and maternal serum screening are described. The need for appropriate prenatal genetic counseling before any diagnostic modality is emphasized.