Less than 20 percent of infants with failure to thrive have an illness that explains their poor weight gain. About 70 percent of cases are due to environmental problem, such as incorrect feeding. About 10 percent of infants are entirely normal.

Causes include:

• Anemia
• Birth defects
• Cerebral palsy
• Child abuse
• Child neglect
• Environmental factors
• Gastrointestinal disease
• Heart disease
• Infections
• Lung disease
• Malabsorption
• Malnutrition