Ten underweight full-term newborns were compared with 10 full-weight newborns on the Brazelton Neonatal Behavioral Assessment Scale. The Brazelton examination differentiated the two groups clearly on the reflexes of walking, crawling and passive movements of arms and legs, and on rooting and sucking. More importantly, it differentiated the two groups on behaviors which are important for the caretaker of the baby: these are attractiveness, need for stimulation, interactive processes and motor processes. The 10 underweight infants were followed up at a later date during the first year. They showed temperamental organizational difficulties and some indication of psychosomatic reaction to stress. It is possible that the underweight newborn's fragile organization elicits anxiety in the caretaker which makes interaction difficult.