The National Institutes of Health estimates that between 135,000 and 200,000 people in the United States have narcolepsy, indicating a rate of less than .01 percent. However, the disorder is widely believed to be underdiagnosed and some researchers believe its true incidence is more likely .02 to .04 percent of the general population. Narcolepsy occurs in roughly similar numbers of men and women, although some research suggests men may be more prone to it.