BACKGROUND: Certain medications are identified by the U.S. Food and Drug Administration (FDA) as class D or X because they increase the risk for birth defects if used during pregnancy. OBJECTIVE: To assess pregnancy rates and the frequency of contraceptive counseling documented with prescriptions for class D or X drugs filled by women of reproductive age. DESIGN: Description of prescriptions filled in 2001. SETTING: A large health maintenance organization in northern California in 2001. PATIENTS: 488,175 women age 15 to 44 years who filled a total of 1,011,658 class A, B, D, or X prescriptions. MEASUREMENTS: Medications dispensed, contraceptive counseling, and pregnancy testing. RESULTS: A class D or X prescription was filled by 1 of every 6 women studied. Women who filled a prescription for class D or X medications were no more likely than women who filled prescriptions for safer, class A or B medications to have received contraceptive counseling, filled a contraceptive prescription, or been sterilized (48% vs. 51% of prescriptions). There was little variation by clinical indication in rates of contraceptive counseling with class D or X prescriptions, except for isotretinoin. Women who filled a class D or X prescription were only slightly less likely to have a pregnancy documented within 3 months than women filling a class A or B prescription (1.0% vs. 1.4% of prescriptions). LIMITATIONS: International Classification of Diseases, Ninth Revision, codes underestimate contraceptive counseling. Documentation of a positive pregnancy test after filling a prescription may overestimate medication use in early pregnancy. Women who filled several prescriptions are overrepresented in prescription analyses. CONCLUSION: Prescriptions for potentially teratogenic medications are frequently filled by women of childbearing age without documentation of contraceptive counseling.