by EBSCO Medical Review Board
(Polysomnogram; Overnight Sleep Study; Rapid Eye Movement Studies)


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:

  • Trouble falling or staying asleep— insomnia
  • Breathing that stops during sleep— apnea
  • Problems falling asleep suddenly during the day— narcolepsy
  • Nightmares and sleepwalking
  • Problems with arm or leg movement during sleep

Possible Complications

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:

  • Any allergies you may have
  • Current medicines, herbs, and supplements that you take and whether you need to stop taking them before the study
  • Foods and drinks you may need to avoid, such as alcohol and items with caffeine
  • How to wash your hair before the study
  • What to wear for the study

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.

CPAP Assistance
Sleep monitor apnea
Copyright © Nucleus Medical Media, Inc.

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.

After Test

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: Accessed March 22, 2021.

Sleep studies. National Heart, Lung, and Blood Institute website. Available at: Accessed March 22, 2021.

Sleep studies: In the sleep laboratory and in the home. American Thoracic Society website. Available at: Updated 2015. Accessed August 22, 2018.

What is a sleep study? Boston Children’s Hospital website. Available at: Accessed March 22, 2021.

Revision Information