The term "failure to thrive" (FTT) has been used for more than 50 years to describe the infant or young child whose growth falls substantially behind that of his or her peers. Currently, the predominant use of FTT is to describe a child's growth failure resulting from caloric or maternal deprivation or both. Despite widespread use, the term FTT lacks a clarified definition. In this study the authors review 22 current reference texts in general pediatrics, pediatric nutrition, and pediatric gastroenterology and 13 recent journal articles addressing FTT. Only 9 of the 22 texts and 9 of the 13 journal articles describe FTT in quantitative terms, but even these references lack consensus on the anthropometric indices used and their criteria for abnormality. The absence of a standard, scientifically credible definition for FTT, which reflects the dynamic nature of this syndrome, continues to produce an ambiguous body of literature on the subject.