Purpose: To evaluate the frequency of preterm infant positions during sleep, and to investigate the association among positions, arousals, sleep patterns, and time of day. Design and Methods: This observational study was conducted in a neonatal unit with 10 preterm infants. Polysomnographic and video recordings during 24 hr identified sleep positions, arousals, sleep patterns, and time of day. Results: Preterm infants were placed most frequently in the supine position (58.4%), followed by right side (24.9%), left side (15.5%), and prone (1.2%). The longest amount of time spent sleeping, and the most frequent number of arousals, occurred in the supine position, followed by prone, left-side, and right-side positions. After controlling for length of time spent in each position, the number of arousals per hour was the greatest in the supine position (13.562 ± 0.732) and least in the prone position (11.56 ± 4.754; p <.001). There were no significant differences in arousals according to position and sleep pattern (indeterminate, quiet, active sleep) or position and time of day (morning, afternoon, twilight, night). Practice Implications: Nurses should evaluate the frequency of preterm infant arousals in each position, and use more often those positions that lead to a lower frequency of arousals and better sleep quality.