The literature on rumination in infancy (the voluntary regurgitation of food and the rechewing and partial reswallowing of it) is reviewed. The stages of rumination are described. The evaluation, hospital course, and successful treatment of an eight-month-old ruminating girl is presented with attention to the vicissitudes of rumination and weight gain correlated with various environmental events that foster or impede an optimum emotional climate. It is postulated that rumination is a manifestation of an infant's overcharged stimulus protective system and represents a failure in development of object relations and a turning inward of libido. Therapy is directed at providing an adequate auxiliary ego for the infant.