Effect of supine and prone flexion position on heart rate, oxygen saturation and pain score of preterm infants Introduction: The study was planned as experimental in order to determine the effect of supine flexion and prone flexion positions, given to preterm infants in Neonatal Intensive Care Unit, on heart rate, oxygen saturation, and pain level. Methods: Study consisted of 46 preterm infants who were in a university hospital between February to November 2014. The effects of two different positions on heart rate, oxygen saturation, and pain were assessed by giving both positions to each infant for 2 hours. Results: It was observed that the heart rate increased in prone flexion position, but oxygen saturation value was similar in both positions. It was observed that pain score decreased on second hour in prone position. Conclusion: The results was showed that infants were influenced by environmental stimuli more in supine flexion position.