BackgroundHepatic pseudoaneurysm (HPA) is a rare complication that can occur after liver trauma and carries a high risk of rupture. HPA is usually asymptomatic until rupture, so performing routine surveillance of liver trauma patients is important. Most posttraumatic HPA occurs within the first week after injury, so surveillance imaging ~ 7 days postinjury is suggested.Case presentationWe herein report a 47-year-old man who was diagnosed with asymptomatic HPA 25 days after a knife injury. The patient was transferred to the emergency room after attempting suicide by stabbing himself in his abdomen with a knife. The knife was surgically removed, and the postoperative course was uneventful. Computed tomography (CT) on postoperative day (POD) 12 showed no HPA. However, follow-up CT on POD 25 revealed HPA. The HPA was treated with coil embolization. The patient was discharged with no complications. One year after the injury, the patient had no recurrence or medical problems.ConclusionWhen managing patients with penetrating liver trauma, it is important to note that HPA may not be identifiable on CT early after injury but may still develop later.