Background <p>Newborns with Neonatal Opioid Withdrawal Syndrome (NOWS) are at risk for smaller size at birth, including weight, length, and head circumference. We hypothesized that children with a history of prenatal opioid exposure and NOWS would have smaller size as infants and toddlers.</p> Methods <p>This retrospective cohort study analyzed a cohort developed from the electronic medical records of all patients who were seen in the NOWS Clinic at a free-standing children’s hospital system through age two years. Anthropometric measurements, demographics, substance and pharmacologic exposures, custodian status and nutritional data were extracted.</p> Results <p>The final sample size included 1190 subjects with 7700 patient encounters. 1153 (97%) had four or more visits in the first two years of life. Forty-four percent of height measurements were below the tenth percentile. Prenatal methadone exposure was negatively associated with later growth. Infants with lower weight, height, and head circumference were prescribed higher caloric density infant formula. Forty percent of the weight measurements were less than the tenth percentile before 6 months, and this improved to 9.3% at 18–25-month visits.</p> Conclusion <p>Children with a history of prenatal opioid exposure are at risk for later short stature. Prenatal methadone exposure specifically is associated with decreased height.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>This large retrospective cohort study found that toddlers with a history of prenatal opioid exposure and Neonatal Opioid Withdrawal Syndrome are at risk for short stature.</p> </ItemContent> <ItemContent> <p>Prenatal methadone, but not buprenorphine, exposure is negatively associated with later growth in children with a history of prenatal opioid exposure.</p> </ItemContent> <ItemContent> <p>The proportion of weight under the tenth percentile improved from infant to toddler ages in children with a history of prenatal opioid exposure.</p> </ItemContent> </UnorderedList></p>