The diameters of the infrarenal abdominal aorta by ultrasonography have not yet been reported in children with cerebral palsy (CP). Because the demand for the surgical applications of the abdominal aorta probably increases in the CP population Owing to their prolonged life-span, we planned a study to assess the diameter of the infrarenal abdominal aorta by ultrasonography in children with CP and to compare them with those of healthy subjects. The study comprised 60 children with CP and 95 age- and sex-matched healthy children. The diameter of the infrarenal abdominal aorta was measured by B-mode ultrasonography. The correlation between the aortic diameter, weight, height, body surface area (BSA), and body mass index was studied. The diameter of the infrarenal abdominal aorta was found to be smaller in children with CP than in healthy children (p < 0.05). There was a significant correlation between the aortic diameter, weight, height, and BSA in both groups (p < 0.05). When a vascular surgical treatment is needed in children with CP, the probability of a small-diameter infrarenal abdominal aorta should be considered.