Plasma citrulline was recently shown to reflect the residual functional enterocyte mass in various situations characterized by intestinal failure. However, few data are available in children with short bowel syndrome. The objective of this study was to assess the value of citrulline assays in this situation. Prospective plasma citrulline assays were performed in 31 children with short bowel syndrome. Median age was 16 mo (range, 1 mo to 15 y), and median follow-up was 14 mo (6-40 mo). The energy supplied by parenteral nutrition (PN), served to assess intestinal failure severity. Plasma citrulline at inclusion showed a positive correlation with residual short bowel length. Subsequent values correlated negatively with intestinal failure severity. Plasma citrulline increased over time during or after weaning from PN (from 15.8 +/- 11.5 microM to 19.3 +/- 3.8 microM) but remained stable and low in patients who continued to need PN (6.5 +/- 3.0 microM at inclusion and 7.7 +/- 6.0 microM at last follow-up). No weaned patients had a residual short bowel length less than 40 cm and plasma citrulline less than 11 microM. Our findings constitute the first evidence that serial plasma citrulline assays help to monitor residual small bowel adaptation in children.