The paper reports the case of a ten-day-old infant presenting to a primary care paediatric clinic with bilious vomiting, abdominal distension and inadequate weight gain. Initial evaluations and daily rectal irrigations led to clinical improvement, while rectal suction biopsies confirmed Hirschsprung disease. Intraoperative biopsies revealed an unexpected ileocolic aganglionosis, diagnosing a rare ‘total colonic aganglionosis’, which required the creation of a temporary ileostomy. This case highlights the importance of early recognition of neonatal intestinal obstruction, timely diagnosis of Hirschsprung disease and the need to consider extensive forms when clinical and preoperative findings are inconclusive.