Both cigarette smoking and alcohol consumption during pregnancy remain an important concern for the practicing obstetrician, who should provide current information on the potential detrimental effects of these habits. There appears to be a wide spectrum of fetal phenotypic response to the effects of alcohol. This phenotypic variability may be partially explained by the dose, timing, and pattern of gestational exposure, the metabolism of mother or fetus, or other environmental and genetic factors. At the most severe end of the spectrum are infants with the unique combination of anomalies termed the fetal alcohol syndrome (FAS). The abnormalities most typically associated with alcohol teratogenicity can be grouped into 4 categories: central nervous system (CNS) dysfunctions; growth deficiencies; a characteristic cluster of facial abnormalites, and variable major and minor malformations. To make a diagnosis of fullblown FAS, abnormalities in all 4 categories must be present. Along the continuum toward normal are infants with various combinations of FAS anomalies. One of the most common and serious defects associated with ethanol teratogenicity is mental retardation. Recent evidence supports the concept of a prenatal origin to the problem. At birth infants with FAS are deficient for both length and weight, usually at or below the 3rd percentile for both parameters. Growth and mental deficiency are seen in many conditions, but the rather striking facial appearance of children with FAS secures the diagnosis. The characteristic face in small children includes short palpebral fissures, short upturned nose, hypoplastic philtrum, hypoplastic maxilla, and thinned upper vermilion. A table lists the variety of malformations that may be found in other organ systems in patients with FAS. The likelihood of miscarriage increases directly with alcohol consumption. Risk of abortion is twice as high in women consuming 1 ounce of absolute alcohol (AA) as infrequently as twice a week. Alcohol has severe effects on a wide variety of animal species, and these effects are reviewed. FAS has been estimated to occur between 1 in 600 and 1 in 1000 live births in the US, France, and Sweden. Possible interference with placentation or implantation has been suggested by the observed increased frequency of spontaneous abortion of a chromosomally normal conceptus for women who smoke. On average, infants born to women who smoke during pregnancy are 200 gm lighter than babies born to comparable women who do not smoke. From a review of these studies, the relationship between smoking and reduced birth weight is independent of all other factors that influence birth weight. The finding of antepartum bleeding of unknown cause has consistently been found more often in smokers, compared with nonsmokers. In almost all studies, the incidence of preeclampsia has been found to be reduced in smokers. Sudden infant death syndrome has been found to be closely associated with both the frequency and level of maternal smoking during pregnancy.