Abstract: BACKGROUND: Small for gestational age (SGA) infants are likely to have decreased placental transfer of opioids and other substances and lower amounts of fat deposition, hence less severe neonatal abstinence syndrome (NAS). The goal of this study is to correlate SGA status and severity of NAS in infants admitted to the neonatal intensive care unit (NICU). METHODS: This is a retrospective analysis of term and late-preterm infants (≥35 weeks gestation) exposed to in-utero substances, born between September 2006 and May 2021, and admitted to an inner-city NICU for medical therapy for NAS. Indicators of the severity of NAS (duration of medical treatment, duration of hospitalization, use of phenobarbital, and use of clonidine) were compared between infants characterized as SGA (birth weight <10th percentile for gestational age) to those not categorized as SGA (non-SGA). RESULTS: A total of 992 infants met the study criteria; 205 (20.7%) in the SGA group and 787 (79.3%) in the non-SGA group. The median duration of medical treatment was significantly lower in infants in the SGA group (22 days vs. 26 days, p = 0.04) and they were less likely to be treated with phenobarbital (19% vs. 26.8%, p = 0.02). CONCLUSION: SGA infants displayed less severe NAS symptoms as indicated by shorter a duration of medical treatment and decreased need for phenobarbital. Our findings may impact decisions around identifying the optimum treatment protocols catered to SGA infants with NAS.