We examined the prevalence of gastrointestinal bleeding in patients undergoing living-related liver transplantation (LRLT). Seventy-seven patients (37 male and 40 female) underwent LRLT at the University of Tokyo Hospital from January 1996 through December 1999. Forty-nine patients were children or adolescents and 28 patients were adults. The mean follow-up period was 21.3 +/- 12.8 months. Nine of the 77 recipients had gastrointestinal bleeding after transplantation. The incidence of posttransplant bleeding was significantly higher in adult recipients than in pediatric recipients (25% vs 4%, P < 0.05). The ratio of graft volume to standard liver volume was significantly lower in adult recipients than in pediatric recipients (41 +/- 6% vs 86 +/- 26%, P < 0.05). Portal vein thrombosis (PVT) developed after LRLT in 8 patients. Variceal bleeding subsequently occurred in all 4 adult patients with PVT but in only 1 of 4 pediatric patients. Small-for-size grafts may cause transient portal hypertension, which increases the risk of gastrointestinal bleeding.