While small bowel transplantation (SBTX) may allow parenteral nutrition independence in the case of short bowel syndrome, its effects on body composition and growth are unclear. For the first time, a paediatric living related SBTX was performed between monozygotic twins. This case report describes their four year nutritional follow up. The 13 year old recipient and his healthy brother underwent measurements of body composition by 50 kHz bioimpedance analysis and bone mineral density of the femoral neck and total femur by dual energy x ray absorptiometry. Xylose tests and measurements of faecal fat evaluated gut absorption. All tests were performed before and after SBTX. Body weight increased from 34.7 to 51.9 kg in the recipient and from 45.0 to 53.2 kg in the donor within four years. The recipient caught up with the height and fat free mass of his brother within two years. Fat mass, and total femur and femoral neck densities are still lower in the recipient than in the donor four years after SBTX (-1.2 kg, -0.087 g/cm(2), -0.035 g/cm(2)). The xylose test of the recipient was still abnormally low after four years (1.37 mmol/l) and faecal fat was high until two years after SBTX (March 2001: 12 g/24 h). The donor always showed normal xylose tests and faecal fat, except for one episode of high faecal fatty acids about 10 months after SBTX. SBTX improved the nutritional state and growth of the graft recipient although body composition, femoral bone mineral densities, and intestinal absorption had not completely normalised after four years.