Given its links with werewolves, vampires and witchcraft, it may not be surprising that the full moon is associated with restless nights.
But now researchers have found scientific evidence that the lunar cycle really does influence sleep.
Just as the myth says, when the full moon is high it is harder to slumber soundly, a study has shown. But the bad night has nothing to do with the moon's eerie glow, or its gravitational influence.
Rather, scientists believe an internal clock that follows the cycles of the moon may be hardwired into our genes.
It ticks away even on the darkest of cloudy nights, when the moon cannot be seen.
"The lunar cycle seems to influence human sleep, even when one does not 'see' the moon and is not aware of the actual moon phase," said psychiatrist Dr Christian Cajochen, from the University of Basel, Switzerland.
His team studied 33 young and old volunteers whose brain waves, eye movements and hormone secretions were monitored as they slept. Around the time of the full moon, brain activity related to deep sleep dropped by 30%, the researchers found.
Participants took five minutes longer than normal to fall asleep, and slept for 20 minutes less time on average during the night. They also showed reduced levels of melatonin, the "body clock" hormone that regulates sleep and wake cycles.
Questioned by the scientists, the volunteers said they felt their sleep was poorer when the moon was full.
The findings are published in the journal Current Biology.