This study aimed to determine the prevalence of septo-optic dysplasia (SOD) in patients with prenatally identified absent cavum septi pellucidi (CSP), agenesis of the corpus callosum (ACC), or dysgenesis of the corpus callosum (DCC).This retrospective chart review investigated neonates prenatally diagnosed with an absent CSP, ACC, or DCC who were admitted to a single quaternary academic medical center in the Pacific Northwest between 2016 and 2023. This prenatal diagnosis prompted a routine and protocolized postnatal workup for SOD including laboratory evaluation, imaging, and specialty consultation. Sociodemographic and clinical data were collected for eligible neonates and their birthing persons. The prevalence of SOD in patients with midline callososeptal anomalies was calculated.Of the 86 patients prenatally diagnosed with absent CSP, ACC, and/or DCC, 36.0% (n = 31) were diagnosed postnatally with SOD. Of those diagnosed with SOD, 71.0% (n = 22) had isolated optic nerve hypoplasia, 9.7% (n = 3) had pituitary hormone abnormalities, and 19.4% (n = 6) had both. Seven patients required maintenance hydrocortisone, one required thyroid hormone replacement, and one required thyroid and growth hormones. Of the 26 patients with SOD who underwent genetic testing, 9 (34.6%) had one or more genetic differences detected.SOD was diagnosed in 36.0% of cases of prenatally diagnosed midline callososeptal anomalies. For patients with prenatally diagnosed midline callososeptal anomalies, a standardized, postnatal SOD evaluation allows timely diagnosis and prompts early intervention and hormone replacement, thus avoiding the consequences of a delayed diagnosis. · Thirty-six percent of patients with midline callososeptal anomalies were diagnosed with SOD.. · Most patients (71.0%) diagnosed with SOD had optic nerve hypoplasia without pituitary abnormalities.. · Although most patients received genetic testing, no findings were linked to SOD..