• weight less than the 5th percentile or an inadequate rate of weight gain
• decreased or absent linear growth ("falling" off the growth chart)
• lack of appropriate hygiene
• subtle to blatant abnormalities in the mother/infant interaction

Diagnosis of FTT begins with a thorough history and physical along with meticulous examination of the patient's growth chart.

When the diagnosis is suspected, important information can often be obtained by admitting the infant to the hospital where, with adequate feeding and care, weight gain and resumed growth can be demonstrated in a matter of days (often as little as 3 or 4 days may demonstrate renewed weight gain).

Other laboratory and imaging studies may be indicated based on the history and physical examination.