The vast majority of information regarding the teratogenicity of new drugs as well as others for which adequate information is not available comes from postmarketing studies. Evaluation by a dysmorphologist of babies prenatally exposed to a particular agent has played an incredibly important role in these studies. Most of the known human teratogens have been identified by the astute clinician approach which involves the observation, documentation, and delineation of individual cases who display a novel phenotype after a particularly rare prenatal exposure. Prospective cohort studies focused on the evaluation of prenatally exposed children who have been ascertained prospectively prior to the known outcome of pregnancy and evaluated by a dysmorphologist for patterns of minor and major malformations have been equally effective. Although most human teratogens have been identified using one of these two methods, both have limitations. The purpose of this study is to set forth the extent to which a careful physical examination performed by a dysmorphologist trained in the identification of minor structural defects in development has added to our knowledge of human teratology and has been instrumental in the identification of new human teratogens. Although dysmorphologists have had a profound impact on our understanding of human teratogens. It is important to recognize that the two approaches outlined in this study must be complemented by other methodologies, such as case–control studies, that more appropriately address risks for major malformations in order to gain the full picture necessary to effectively counsel women about safety of drugs during pregnancy. © 2011 Wiley-Liss, Inc.