Background <p>Preduodenal portal vein is a rare anatomical abnormality in which the portal vein passes anteriorly relative to the duodenum instead of posteriorly. It is believed to occur during embryonic development and is commonly associated with other congenital anomalies.</p> Case Presentation <p>In this case report we discuss a 3-day-old male patient, presenting with symptoms consistent with gastric outlet obstruction.</p> <p>An initial plain abdominal radiograph demonstrated an abnormally situated right sided gastric bubble, with an upper gastrointestinal contrast study confirming situs inversus with a markedly dilated stomach and dilated first part of the duodenum.</p> <p>Subsequently the patient was taken to theatre, with intraoperative findings of preduodenal portal vein causing duodenal obstruction, which was managed surgically with gastro-duodenostomy.</p> Conclusion <p>This case contributes to limited existing literature on a rare congenital abnormality; it highlights the importance of considering preduodenal portal vein as a potential contributor to congenital duodenal obstruction, especially in cohorts found to have additional anatomical variants such as situs inversus, as it is recognised that preduodenal portal vein often occurs as part of a syndromic collection of anatomical anomalies.</p>