Failure to thrive is a complex medical disorder characterized by impaired growth and often accompanied by developmental delay. The etiology of failure to thrive may be an organic problem, psychosocial factors within the environment, or a combination of both. The etiology of organic failure to thrive is a medical or constitutional problem. Nonorganic failure to thrive has been associated with various psychosocial factors, including disturbances in parent-child interaction and difficult infant temperament. As a member of the interdisciplinary medical team, the occupational therapist contributes to both the diagnosis and treatment of organic and nonorganic failure to thrive.