Research on the development of preterm infant feeding behavior has focused mainly on bottlefeeding, using invasive methods or observations by professionals. In this study, a clinical method for observing breastfeeding was developed in collaboration between observers and mothers for the purpose of enabling neonatal personnel and mothers to describe developmental stages in preterm infant breastfeeding behavior. Tests of interobserver reliability resulted in acceptable agreement between observers, but a somewhat lower level of agreement between observers and mothers. The scale showed a good capacity to discriminate between infant gestational ages and can be used for helping mothers to identify their infants' emerging competence.