(Polysomnogram; Overnight Sleep Study; Rapid Eye Movement Studies)
How to Say It: Pol-ee-som-NAH-grah-fee
by Cynthia M. Johnson, MA
Polysomnography (PSG) is a study of sleep cycles and sleep behavior. It is usually done in a sleep center overnight. This study involves observing a person at sleep while charting brain waves and other body functions.
Reasons for Test
This study is done to evaluate sleeping problems, such as:
There are no major, lasting problems from having this test.
What to Expect
Prior to Test
The care team may meet with you to talk about:
Description of Test
You will arrive in the evening. You will be given time to relax in the room where you will sleep. Electrodes will be attached to your head, legs, and chest. Other monitors will be placed around your chest, near your nose and mouth, and on your finger. You will be able to read and relax until your bedtime.
For most of the night, you will be able to move and turn during sleep. But, you may be asked to try to sleep in a certain position for part of the night. You will be watched by video during the night. This will be done to make sure that the electrodes do not come loose. They can also be taken off to use the bathroom. Sometimes, the test may show that you can benefit from a certain treatment, such as continuous positive airway pressure (CPAP). This may be started midway through the night.
The doctor may ask for an additional test for narcolepsy. This is known as the Multiple Sleep Latency Test (MSLT). You will need to stay for part of the next day. You will be asked to nap for up to 20 minutes every 2 hours. The time it takes you to fall asleep and the time it takes you to go into deep sleep will be measured.
The electrodes will be removed in the morning. Most people will be able to go home.
How Long Will It Take?
About 10 to 12 hours
Will It Hurt?
Results from this test may be ready right away or within two weeks. Your doctor will go over the results and discuss them with you.
Problems to Look Out For
There should not be side effects or lasting problems from this study. Call your doctor if you have any concerns.
If you think you have an emergency, call for medical help right away.
American Academy of Sleep Medicine
National Sleep Foundation
Better Sleep Council Canada
Canadian Sleep Society
Kushida CA, Littner MR, et al. American Association for Sleep Medicine practice parameters for the indications for polysomnography and related procedures: an update for 2005. Sleep. 2005 Apr;28(4):499-521.
Polysomnography. EBSCO DynaMed website. Available at: https://www.dynamed.com/evaluation/polysomnography. Accessed March 22, 2021.
Sleep studies. National Heart, Lung, and Blood Institute website. Available at: https://www.nhlbi.nih.gov/health-topics/sleep-studies. Accessed March 22, 2021.
Sleep studies: In the sleep laboratory and in the home. American Thoracic Society website. Available at:
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Updated 2015. Accessed August 22, 2018.
What is a sleep study? Boston Children’s Hospital website. Available at: https://www.childrenshospital.org/conditions-and-treatments/treatments/sleep-studies. Accessed March 22, 2021.
Last reviewed December 2020 by EBSCO Medical Review Board Daniel A. Ostrovsky, MD