Failure to thrive is a presenting symptom, rather than a diagnosis. Organic failure to thrive may be caused by defects in food assimilation, excessive loss of ingested calories, increased energy requirements or prenatal insults. Nonorganic failure to thrive may occur accidentally, or it may be related to economic or emotional deprivation, as well as to child abuse or neglect. Assessment of a child with failure to thrive includes a comprehensive history and a thorough physical examination. Some basic laboratory screening tests may be helpful in the evaluation. More extensive investigation may be required, based on the clinical findings and the results of the initial screening tests. Early intervention is essential, because children may develop significant long-term sequelae from nutritional deficiency.