The developing organism is unique in its responsiveness to drugs and predictability of therapeutic effectiveness based on the adult can lead to grave consequences in the neonate and child. It should be emphasized that fetal adverse drug effects are not always manifested immediately as in the case of maternal thalidomide ingestion. It is important to note that fetal abnormalities can occur after several months as seen with clonidine or in the case of diethylstilbestrol vaginal adenocarcinoma can take 20 years to develop. Based on limited reported effects in humans and more extensive studies with animals, drugs are classified as to the risk of induction of fetal toxicity in categories ranging from A (safe) to D (contraindicated in pregnancy). A separate extremely toxic category X is also used. Although the pregnant mother may require treatment of certain disorders, there are a number of drugs which are absolutely contraindicated including those agents in risk category X and the socially unacceptable drugs of abuse. A limited use for drugs in category D under close supervision may be necessary. Prescribed drug use in pregnancy should be dissuaded. Further ingestion of over-the-counter (OTC) preparations should be limited and deemed to be used with caution. It is generally accepted that the pregnant mother provides a fetus an environment in which to develop. However, drug exposure in utero is far more deleterious than in the growing child as the fetus lacks the ability to cope with pharmaceutical agents entering its biosphere.