Two 13-year-old monozygotic twins were used for living related small bowel transplantation (SBTx). The recipient presented with short gut syndrome secondary to complicated abdominal surgery. The indication for SBTx was based on a failure to thrive and a poor tolerance of TPN. The donor was an identical twin, as demonstrated by skin graft acceptance, which allowed performance of SBTx without immunosuppression. Growth charts were used to follow intestinal absorption functions and body composition. The donor was used as a control for the recipient. The recipient, who was transplanted with 160 cm of donor ileum, was discharged on postoperative day 62 on a regular diet. Before SBTx the recipient was 10 kg lighter in body weight than the donor, a gap that was progressively reduced over the follow-up period. A height deficit of 3 cm reversed within 1 year after SBTx. A 10-kg deficit in fat-free body mass was completely extinguished within 18 months. By 18 months posttransplant, recipient serum albumin and prealbumin were normal and comparable to donor values. d-Xylose absorption in the recipient remained lower than that in the donor. Within 6 months fecal fat excretion normalized in the recipient. d-Xylose absorption and fecal fat excretion were always within a normal range in the donor.