SUMMARY Rationale: Fifty-six percent of patients with Obstructive Sleep Apnea (OSA) are position dependent, defined as having an AHI, which is at least twice as high in supine sleeping position compared to the AHI during sleep in other positions. Standard therapy for patients having mild or moderate POSA is treatment with an Oral Appliance Trainer (OAT). Recently a new device Sleep Position Trainer (SPT) is been introduced especially for patients with POSA.