Background and ObjectiveaaPatients with position-dependent obstructive sleep apnea have a > 2-fold higher apnea-hypopnea index when sleeping in a supine position compared with a nonsupine position. We investigated the effect of body pillow use on sleeping body position and sleep architecture in healthy young adults. MethodsaaIn experiment 1, we evaluated the body pressure distribution with or without body pillow use in 8 healthy young adults [age, 36.5 ± 13.0 years; body mass index (BMI); 20.6 ± 1.2 kg/ m 2 ]. In experiment 2, we performed a randomized-crossover intervention study to evaluate the effects of body pillow use on sleeping position and sleep architecture in 10 healthy young adults (age, 24.3 ± 7.8 years; BMI, 21.4 ± 1.7 kg/m 2 ). Sleep architecture was characterized by polysomnography, and body positions were monitored using a sensor. Subjective sleep quality was evaluated with the Oguri-Shirakawa-Azumi sleep inventory, middle age and aged version. ResultsaaIn experiment 1, body pillow use significantly reduced mean body pressure on the shoulder, hip, and whole body. In experiment 2, mean time spent in the supine, lateral, and prone body positions did not differ significantly between the 2 trials. Body pillow use, however, significantly extended the sustained time spent in the lateral body position compared with the control trial. Subjective sleep quality and sleep architecture did not differ significantly between the 2 trials, but body pillow use decreased the number of short (30 s) slow-wave sleep episodes. ConclusionsaaSleeping with a body pillow effectively extends sustained time in a lateral sleeping position and prevents segmentation of slow-wave sleep episodes.