To measure activity during sleep, polysomnography and actigraphy are often used. The DynaPort MiniMod measures movement intensity and body position day and night. The goal was to examine the validity of the DynaPort MiniMod in assessing physical activity and body posture during sleep. In Study A, 10 healthy participants slept with the DynaPort MiniMod and the Actiwatch for one night. In Study B, 8 participants suspected of having Obstructive Sleep Apnoea Syndrome slept for one night with the DynaPort MiniMod and underwent complete polysomnography as part of the typical care protocol. In Study A, there was a significant moderate correlation (r=.70) between the movement scores of the Actiwatch and the DynaPort MiniMod. In Study B, a high intraclass correlation (r=.84) between body posture scores of the DynaPort MiniMod and the polysomnography position sensor was observed. The DynaPort MiniMod is a valid measurement device for physical activity during sleep.