The portal vein is the main source of blood and hepatotrophic factors to the liver. Partial portal-vein ligation in rats results in reduced growth compared with that in control rats. To investigate whether extrahepatic portal vein obstruction occurring in early childhood influences growth in humans, anthropometric and nutritional assessments were prospectively carried out in 61 patients with extrahepatic portal vein obstruction. Comparisons were made with 183 matched healthy controls using National Center of Health Statistics reference. Fifty-one percent of children with extrahepatic portal vein obstruction had stunted growth (height for age <90% of normal), compared with 16% of controls (p < 0.01). Growth retardation was severe in patients with longer (>5 yr) than with shorter (<2.5 yr) duration of clinical portal hypertension (height for age, 88.0 ± 3.2 vs. 95.1 ± 3.0; p < 0.01). Little difference was seen in the energy intake (1,302 ± 463 kcal/day vs. 1,335 ± 449 kcal/day; p = not significant) and weight for height index (83.6 ± 9.3 vs. 88.0 ± 7.9; p = not significant) between extrahepatic portal vein obstruction patients and controls. This suggested that despite comparable nutrition, marked growth retardation occurred in extrahepatic portal vein obstruction patients. Incremental growth velocity was studied in 31 patients; in 24 (73%) the baseline Z score (-2.1 ± 0.2) had decreased further (-2.4 ± 0.2) at the end of follow-up (15.5 ± 1.6 mo). Although the incremental height velocity was only 56% of the expected height, incremental weight gain was 98% of the expected weight for the attained height. This indicates linear growth failure despite optimal nutrition. In conclusion, our results demonstrate that most children with extrahepatic portal vein obstruction have marked growth retardation and diminished growth velocity. The roles of hemodynamic and hormonal factors in modulation of growth in young extrahepatic portal vein obstruction patients must be studied. (HEPATOLOGY 1992;15:229–233).