OBJECTIVE: To estimate the burden of exposure to medications associated with known or suspected risk of fetal harm among pregnant women in Regione Emilia-Romagna (RER), Italy.Methods: A prevalence study was conducted using the RER healthcare database, including data for the entire RER population of about 4 million inhabitants.  Female residents of RER who delivered a baby in a hospital between January 1, 2004 and December 31, 2004 were identified via ICD-9-CM codes.  All prescription drug data were reviewed for the 270 days leading up to date of delivery.  Drugs were grouped into pregnancy risk categories (A, B, C, D, X) using established classification systems.  Contraindicated drugs were defined as category X drugs and potentially dangerous drugs were defined as category D drugs.  Women exposed to contraindicated and potentially dangerous drugs in the 270 days prior to delivery were identified. Results: Among the 33,343 deliveries identified in 2004, 70% were exposed to at least one prescription medication in the 270 days prior to delivery.  Approximately 1% of women were exposed to drugs contraindicated in pregnancy (category X), including 189 women (0.6%) receiving these drugs during the first trimester.  Approximately 1.5% of women were exposed to potentially dangerous (category D) drugs.  Measurable proportions of women were exposed to ACE-inhibitors (0.79%) and HMG-CoA reductase inhibitors (0.28%), which have recently been linked to risk of fetal malformations.   Conclusions: For the entire RER population, nearly 1 in every 100 pregnant women was prescribed a medication associated with risk that potentially outweighs possible benefit according to established pregnancy risk classification systems.  The medical care system needs to address this serious public health problem and focus on the most commonly prescribed drugs associated with fetal harm among pregnant women because prevention of these exposures may have the greatest public health impact with respect to drug-related teratogenicity.