Objective:To determine the frequency and risk factors of small-for-gestational-age newborns in a high-risk maternity.Methods:This is an observational, cross-sectional, and case-control study, conducted in a public tertiary care maternity hospital. Data from 998 newborns and their mothers were collected through interviews and review of medical records and prenatal care cards. Some placentas underwent histopathological analysis. The variables of small-for-gestational-age and non-small-for-gestational-age newborns and of their mothers were statistically compared by means of Student's t test, Fisher's exact test, and odds ratio. The significance level used was 0.050.Results:There was a 17.9% frequency of small-for-gestational-age newborns. The statistically significant factors associated with the birth of these babies were female sex (p=0.012); positive history of another small-for-gestational-age child (p=0.006); inadequate prenatal care (p=0.019); smoking (p=0.003); hypertensive disorders of pregnancy (p=0.007); placental bleeding (p=0.009) and infarction (p=0.001).Conclusion:In the population studied, the frequency of small-for-gestational-age newborns was high and associated with sex, inappropriate prenatal care, presence of maternal diseases and addictions, and placental abnormalities.