Prenatal exposure to alcohol is associated with a spectrum of abnormalities, referred to as the Fetal Alcohol Spectrum Disorders (FASD). Alcohol measurement issues have created many challenges in understanding the patterns of alcohol exposure that result in FASD. Knowledge about prenatal alcohol volume and timing of exposure in relationship to fetal outcomes improves our understanding of the magnitude of risk with various patterns of drinking. Using data on 992 subjects collected prospectively in California between 1978 and 2005, we examined the patterns and timing of alcohol exposure in relation to the characteristic features of FAS and to minor structural malformations that occurred in at least five percent of the sample that were not previously established as the characteristic features of FAS. A dysmorphologist performed a blinded physical examination of each infant for the presence or absence of minor structural malformations using a standard checklist of 132 minor malformations. In addition to the minor malformations, a number of anthropometric parameters were measured. Patterns of drinking were evaluated by drinks per day, number of binge episodes, and maximum number of drinks. Timing of exposure was evaluated 0-6 weeks post-conception, 6-12 weeks post-conception, second trimester, and third trimester. Logistic and poisson regression models were developed to test both hypotheses. Reduced birth length and weight, microcephaly, smooth philtrum, thin vermillion border, and naevus flammeus neonatorum are associated with specific gestational timing of prenatal alcohol exposure and are dose-related without evidence of a threshold. Additionally, poisson regression models of the alcohol-related outcomes showed that during the first two trimesters, as the number of drinks per day on average increased and the number of binge episodes increased, the number of alcohol-related birth outcomes significantly increased (p's<0.001). As the maximum number of drinks in one occasion increased throughout pregnancy, the number of outcomes also significantly increased (p's<0.01). There is no safe threshold for alcohol consumption during pregnancy. Based on the results of this study, pregnant women should continue to abstain from alcohol consumption. Additionally, women who are of childbearing age and who are contemplating or at risk of becoming pregnant should be encouraged to avoid drinking.