Lead author Dr. Maurice Ohayon, professor of psychiatry and behavioral sciences at the Stanford University School of Medicine, found about 3.6 percent of U.S. adults -- or upward of 8.4 million -- are prone to sleepwalking.
Ohayon and colleagues used phones surveys of 19,136 individuals from 15 states involving mental health, medical history and medication use.
Participants were asked specific questions related to sleepwalking, including frequency of episodes during sleep, duration of the sleep disorder and any inappropriate or potentially dangerous behaviors during sleep.
The researchers determined as much as 3.6 percent of the sample reported at least one episode of sleepwalking in the previous year, with 1 percent saying they had two or more episodes in a month.
"There is no doubt an association between nocturnal wanderings and certain conditions, but we don't know the direction of the causality," Ohayon said in a statement. "Are the medical conditions provoking sleepwalking, or is it vice versa? Or perhaps it's the treatment that is responsible."
The study published in the journal Neurology also found the duration of sleepwalking was mostly chronic, with just over 80 percent of those who have sleepwalked reporting they've done so for more than five years.