There is significant variability in severity of neonatal abstinence syndrome (NAS) due to in utero opioid exposure. Our previous study identified single nucleotide polymorphisms (SNPs) in the prepronociceptin (PNOC) and catechol-O-methyltransferase (COMT) genes that were associated with differences in NAS outcomes. This study looks at the same SNPs in PNOC and COMT in an independent cohort in an attempt to replicate previous findings.