Studies of behavioral diagnosis in children with nonorganic failure-to-thrive (NOFTT) are critically reviewed. Prior studies have been based on several problematic assumptions: (1) specific behavioral abnormalities are associated with NOFTT, (2) NOFTT is a homogeneous population, and (3) a strict dichotomy between organic and environmental influences on physical growth is a valid distinction. An alternative way to organize data from behavioral assessment is presented which emphasizes the heterogeneity of NOFTT and the consequences of environmental and biologic risk factors on psychological development. A comprehensive approach to behavioral assessment can facilitate the clinical management of NOFTT and encourage research concerning the developmental processes which affect the psychological outcomes of NOFTT children.