Background <p>Umbilical vein catheterization is relatively straightforward procedure because the vein is easily recognized as a single, large, thin-walled vessel. However, anomalies of the umbilical vessels, such as the multivessel cord, which embeds more than two arteries or more than one vein, can result in catheter misplacement.</p> Case presentation <p>We present a unique case of a supernumerary patent umbilical artery in an asphyxiated term neonate, which resulted in the misplacement of the umbilical venous catheter in one of the three arteries. The diagnosis of artery cannulation was made through a comprehensive analysis of the patient’s blood gases, the use of a pressure transducer to confirm the presence of a pulsatile arterial signal, and the interpretation of a chest X-ray. Subsequently, the catheter was removed without complication. A more detailed examination of the umbilical cord revealed the presence of three arteries and a vein, which was then successfully cannulated.</p> Conclusions <p>This case reinforces the notion that the umbilical cord may include more than three vessels, and that umbilical vein cannulation requires prior meticulous observation of the number of vessels to prevent misplacement of the catheter.</p>