Spinal subarachnoid hematoma may result in sequelae such as bilateral lower extremity paralysis and vesicorectal disturbances. Although spinal subarachnoid hematoma is rare in infants, early intervention has been suggested to improve neurological prognosis. Therefore, clinicians are encouraged to make early diagnosis and surgical intervention.A 22-month-old boy was prescribed aspirin for a congenital heart disease. A routine cardiac angiography was performed under general anesthesia. Fever and oliguria developed on the next day, followed by flaccid paralysis of the lower limbs four days later. Five days later, he was diagnosed with spinal subarachnoid hematoma and associated spinal cord shock. Even after emergent posterior spinal decompression, hematoma removal, and rehabilitation, the patient remained with bladder rectal disturbance and flaccid paralysis of both lower limbs.Diagnosis and treatment of this case were delayed mainly because of his difficulty to complain of back pain and paralysis. The neurogenic bladder was one of the first neurological symptoms in our case, so it may be important to consider spinal cord involvement in infants with bladder compromise.Risk factors for spinal subarachnoid hematoma in infants are largely unknown. The patient had undergone a cardiac angiography the day before the onset of the symptoms, which may be related to subarachnoid hematoma. However, similar reports are scarce, with only one case of spinal subarachnoid hematoma reported in an adult following cardiac catheter ablation. Accumulation of evidence regarding risk factors for subarachnoid hematoma in infants is warranted.