Small-intestine length from ligament of Treitz to ileocecal valve was measured in 183 infants and children ranging up to 15 years of age. Elongation of the intestine was rapid until crown-heel length was 60 cm and remained constant from 100 to 140 cm of body length. When patients were placed into three general diagnostic categories (congenital heart disease, abdominal lesions, and miscellaneous) no significant differences were found. However, several striking instances of abnormally long or short small intestines were encountered.