The emergence of consolidated nighttime sleep and the formation and maintenance of parent-infant relationships are 2 primary developmental achievements of the infancy period. Despite the development of a transactional model that links parenting behaviors to infant sleep, limited attention has been devoted to examining experimental manipulations of infant sleep that may impact the discrete parent-infant interactions that may form the foundation for emerging attachment relationships. In the present study, infants were randomly assigned to wear high-absorbency disposable diapers or to continue using traditional low-absorbency cloth diapers that necessitate frequent changes and associated disruptions of nighttime sleep. Parents reported on infant sleep before and during the 6-week experimental manipulation; a subset of infants also wore actigraphs. Parents and infants also participated in a parent-infant interaction task both before and near the end of the experimental manipulation. Infants who wore cloth diapers experienced more frequent sleep disruptions overall as well as a greater number of disruptions that did and did not wake the infant from sleep. Infants who wore disposable diapers were rated as experiencing more engagement and positive affect near the end of the intervention relative to infants who wore cloth diapers; mothers of infants who wore disposable diapers were rated as more engaged and sensitive near the end of the intervention relative to mothers of infants who wore cloth diapers. These findings suggest that the disposable diaper manipulation was causally related to characteristics of mother-infant interactions that may form the foundation for emerging attachment relationships.