OBJECTIVE To identify important factors that influence mothers' perceptions of engaging in exercise with their preterm infants. DESIGN Qualitative, semistructured individual interviews. SETTING Neonatal Intensive Care Unit. PARTICIPANTS Thirteen mothers of preterm infants who were in the Neonatal Intensive Care Unit. METHODS Two researchers conducted interviews with mothers in English or Spanish. Interviews were recorded, transcribed, and analyzed. RESULTS Mothers tended to view infant exercise as beneficial but feared for the safety of their infants. They perceived nurses as experts who could safely exercise their infants but feared that they themselves might harm their infants. Factors that influenced their beliefs included previous experiences with infant exercise and views regarding the fragility or the strength of their own infants. Mothers identified nurses, doctors, family members, and research studies as trusted sources of information on exercise efficacy and safety. CONCLUSION Understanding and addressing mothers' perceptions is a crucial component of a nursing intervention that teaches parents to do assisted exercises at home with their preterm infants.