Object: The pulmonary arterial (PA) growth following a Fontan procedure tends to be suboptimal to the somatic growth. The purpose of this study is to investigate whether a small PA affects the late outcome of the Fontan procedure. Methods: This is a cross sectional study on the 120 Fontan patients who have undergone the Fontan procedure from 1986 to 2003. PA size was measured by cardiac CT. Their mean age was 19.3짹5.6 years and the elapsed time after Fontan operation was 12.8짹3.7 years. The patients were divided into three groups according to the PA index (Nakada index): PAI < 180 mm2/m2 (group I: N = 39, 148짹23 mm2/m2), 180 mm2/m2 ��� PAI < 250 mm2/m2 (group II: N = 56, 216짹22 mm2/m2) and PAI ��� 250 mm2/m2 (group III: N = 25, 308짹60 mm2/m2). The data on the hemodynamics and exercise performance were analyzed. Results: There was no difference on the occurrence of protein losing enteropathy and hepatic change among the three groups. The cardiac catheterizations showed no difference in hemodynamics such as the pressure of Fontan pathway, ventricular end-diastolic pressure and arteriovenous oxygen difference. Peak oxygen consumption (VO2) was 28.3짹5.0 in group I, 27.7짹6.0 in group II and 29.2짹8.2 (ml/kg/min) in group III (p = 0.739) during cardiopulmonary exercise test. Oxygen consumptions at aerobic threshold were not different among three groups. Systolic BP during maximal exercise was 142.6짹21.6 in group I, 145짹23.2 in group II, and 152.1짹38 (mmHg) in group III (p = 0.740). However BNP was significantly higher in group III (168.8짹264.5) than that in group I and II (50.0짹46.6 and 70.6짹119.6 (pg/ml) respectively, p = 0.15). Conclusion: The pulmonary artery size affects neither late outcome nor functional status after a Fontan operation.