EXECUTIVE SUMMARY: Positioning of preterm infants is a basic task of neonatal nursing care. A variety of outcomes are affected by different body positioning of preterm infants. This review evaluates the clinical evidence of the effects of positioning of preterm infants with regard to physiological outcomes and sleep states. OBJECTIVES: To conduct a systematic review to determine the best available evidence related to the positioning of preterm infants. The specific review questions addressed were: the physiological outcomes affected by different positioning, and the best position for promoting sleep. CRITERIA FOR CONSIDERING STUDIES FOR THIS REVIEW: This review considered all studies that included infants born before 37 weeks of gestational age in any hospital setting. Outcomes included measures for physiologic effects and sleep state. The review primarily considered any randomized clinical trails (RCTs) that explored different positions in preterm infant but also included quasi-experimental designs. SEARCH STRATEGY FOR IDENTIFICATION OF STUDIES: The search sought to find published and unpublished studies. The database search included: Pubmed, CINAHL, ProQuest, EMBASE, Science Direct, and Dissertation Abstracts International. Studies were additionally identified from reference lists of all studies retrieved. ASSESSMENT AND DATA EXTRACTION: All studies were checked for methodological quality by two reviewers and data was extracted using tools developed by the Joanna Briggs Institute. DATA ANALYSIS: The study results were pooled in statistical meta-analysis using Review Manager Software and summarized in narrative form where statistical pooling was not appropriate or possible. RESULTS: Thirty two studies were included in the review. The results of this review support the prone position in preterm infants for improvement of arterial oxygen saturation, improved lung and chest wall synchrony of respiratory improvements, decreased incidence of apnea in infants with a clinical history of apnea, promoted sleep, and decreased gastroesophageal reflux. However, the prone position increased postural abnormalities, orthopaedic abnormalities of the feet, and delayed developmental musculature. The combined use of a postural support roll and a postural nappy while very preterm infants are nursed, improved hip and shoulder posture up to term postmenstrual age. The change in body position from horizontal to head-up tilt in very immature and unstable infants may affect the cerebral homodynamic. The management of position per se may not be sufficient for assisting preterm neonates to cope with the painful procedure. Furthermore, preterm infants are susceptible to oxygen desaturation in car seats and carrying slings. CONCLUSION: Prone positioning was shown to have many advantages for prematurely born infants. But the longer, deep sleep period and fewer awakenings associated with a prone position would support higher vulnerability for preterm infants to sudden infant death syndrome (SIDS). Therefore, all preterm infants placed in the prone position should have continuous cardio-respiratory and oxygen saturation monitoring. Preterm infants should be placed in a properly supported position to ensure functional support of all parts of the body as well as ensuring physical safety. In addition, preterm infants should not be left unattended in car safety seats and carrying slings.