Data were abstracted from the medical and social work charts of 20 newborns who were classified as boarder babies and their mothers (N = 18) to identify bio-psycho-social factors associated with boarding. The findings show that the mothers whose newborns remained in the hospital as boarders were usually drug users, had other children in out-of-home placement, and over half are periodically homeless. Most of these mothers also lacked informal social support. The major health problems of infants were prematurity and associated infections. The total number of infant boarding days was 195 for a total of $117,000 in unreimbursed costs to the hospital. Practice and program implications and directions for future research are discussed.