• Infants and children with suspected caloric-deprivation failure to thrive (CDFTT) are commonly hospitalized to confirm the diagnosis. In the hospital, weight gain at an accelerated rate is used as the primary diagnostic criterion. We evaluated how soon patients with CDFTT began to gain weight and if the speed with which the patients started to gain weight was age dependent. Of 476 patients with growth problems, 57 met the criteria for inclusion in the study. We developed the concept of the "growth quotient," which expresses the patient's rate of growth. We found that almost all 57 children started to grow in less than two weeks, and those less than 6 months old usually began to gain weight in only two to three days. Older infants and children with CDFTT often had initial corrective growth rates equal to or greater than those of young infants.