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  • Cynthia M. Johnson, MA
Publication Type:



(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

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.

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

The test is given in the evening after some time to relax. Electrodes are attached to the head, legs, and chest. Other monitors are placed around the chest, near the nose and mouth, and on the finger.

For most of the night, the test is done in the person's normal sleep position. But, part of the test may be done in a certain sleep position. The person sleeping is watched by video. 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 the need for a certain treatment, such as continuous positive airway pressure (CPAP). This may be started midway through the night.

CPAP Assistance.

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The doctor may ask for an additional test for narcolepsy. This is known as the Multiple Sleep Latency Test (MSLT). This involves staying for part of the next day. The person will be asked to nap for up to 20 minutes every 2 hours. The test will measure the time it takes to fall asleep and the time it takes to go into deep sleep.

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 a few weeks. The doctor will discuss the results.





  • Kapur VK, Auckley DH, et al. Clinical Practice Guideline for Diagnostic Testing for Adult Obstructive Sleep Apnea: An American Academy of Sleep Medicine Clinical Practice Guideline. J Clin Sleep Med. 2017;13(3):479-504.
  • 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;28(4):499-521.
  • Polysomnography. EBSCO DynaMed website. Available at: https://www.dynamed.com/evaluation/polysomnography.
  • Sleep studies. National Heart, Lung, and Blood Institute website. Available at: https://www.nhlbi.nih.gov/health/sleep-studies.
  • Sleep studies: In the sleep laboratory and in the home. American Thoracic Society website. Available at: http://www.thoracic.org/patients/patient-resources/resources/sleep-studies.pdf.
  • What is a sleep study? Boston Children’s Hospital website. Available at: https://www.childrenshospital.org/treatments/sleep-studies.


  • Daniel A. Ostrovsky, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.