Prevalence increases from ages 10 to 13 for both males and females but continues to in-
crease to ages 20–29 for females (while decreasing for males), when it can be twice as high
for females as for males. Prevalen ce decreases steadily with age for both sexes, but the gen-
der difference remains. Among adults, prevalen ce of nightmares at least monthly is 6%,
whereas prevalence for frequent nightmare s is 1%–2%. Estimates often combine idio-
pathic and posttraumatic nightmares indiscriminately.
Development and Course
Nightmares often begin between ages 3 and 6 years but reach a peak prevalence and se-
verity in late adolescence or  early adulthood. Nigh tmares most likely appear in children
exposed to acute or chronic psychosocial stressors and thus may not resolve spontane-
ously. In a minority, frequent nightmares pers ist into adulthood, becoming virtually a life-
long disturbance. Although specific nightm are content may reflect the individual’s age,
the essential features of the diso rder are the same across age groups. 
Risk and Prognostic Factors 
Temperamental. Individuals who experience nightmares  report more frequent past ad-
verse events, but not necessarily trauma, an d often display personality disturbances or
psychiatric diagnosis. 
Environmental. Sleep deprivation or fragmentation, and irregular sleep-wake schedules
that alter the timing, intensity,  or quantity of REM sleep, can put individuals at risk for
nightmares.
Genetic and physiological. Twin studies have identified genetic effects on the disposi-
tion to nightmares and their co-occurrence with other parasomnias (e.g., sleeptalking). 
Course modifiers. Adaptive parental bedside behaviors, such as soothing the child fol-
lowing nightmares, may protect agai nst developing chronic nightmares.