Yawning has been observed in foetuses and preterm infants. The aim of this study was to assess the frequency and the 24 h distribution of yawning in preterm infants. Twelve low-risk infants between 31 and 40 weeks of post-conceptional age (PCA) were continuously video-recorded for 24 h in their incubator. Spontaneous yawning was defined as opening of the mouth to its full extension in a dramatic stretch movement. The results showed that the rate of yawning across the 24-h period was 1.10/h. The highest incidence of yawns was in the waking motility pattern when compared to active sleep or quiet sleep motility patterns. Between 31 and 40 weeks, yawn incidence significantly decreased mainly during the day. The marked decrease in yawn frequency with age may be related to the development of circadian and homeostatic control of sleep and wake.