The relationship between caloric insufficiency and impaired growth in children with chronic inflammatory bowel disease has been increasingly recognized in recent years. The mechanism by which nutritional insufficiency leads to decreased growth in these children is unclear. Our study suggests that chronic undernutrition lowers circulating somatomedin-C, which is known to exert anabolic effects on peripheral tissues. Therapeutic intervention that increases caloric intake results in improved somatomedin-C levels and growth velocity. Monitoring somatomedin-C levels in growth-impaired children with inflammatory bowel disease provides an important marker of nutritional sufficiency and reversibility of growth retardation.