This article reports the results of a national mail survey of practicing obstetricians and pediatricians who see neonates (response rate, 63%). More than 70% reported having ever suspected prenatal substance abuse; 27% reported they had never suspected it. The most common lifetime pattern (60%) was some response whenever prenatal substance abuse was suspected; just over 10% had a discretionary response, acting in some cases but ignoring others; 2% consistently ignored their suspicions. Getting help for the patient and protecting the fetus were the most common reasons to act. Among physicians who ignored their suspicions, lack of sufficient evidence of substance use was the reason cited most often. Obstetricians are far more likely to provide the patient with information and get a substance abuse history, and pediatricians are more inclined to involve outsiders; but both seem quite willing to act on their suspicions of prenatal substance abuse and generally respond by taking positive actions.