Failure to thrive (FTT) is a meical term which denotes poor weight gain and physical growth failure over an extended period of time in infancy. The term has been in medical use for over a century. As used by pediatricians, it covers poor physical growth of any cause and does not imply abnormal intellectual, social, or emotional development. Failure to thrive is weight consistently below the 3rd to the 5th percentile for age, progressive decrease in weight to below the 3rd to the 5th percentile, or a decrease in the percentile rank of 2 major growth parameters in a short period. The cause may be an identified medical condition or related to environmental factors. Both types relate to inadequate nutrition. Treatment aims to restore proper nutrition.