IntroductionThis study examined the efficacy of a five-module cognitive behavioral therapy for nightmares in children (CBT-NC) and improving sleep.Materials and methodsForty-six youth aged 6–17 years with sleep problems and at least weekly chronic and distressing nightmares were randomized to treatment (n = 23) or waiting list (n = 23) using a block four randomized design. Among participants, 65% (n = 30) were White, 4% (n = 2) were Black/African American, 2% (n = 1) were Asian American, 13% (n = 6) were Native American or Pacific Islander, and 15% (n = 7) were multiracial. Fifty percent of participants (n = 23) were cisgender girls, 35% were cisgender boys (n = 16), 7% were transgender boys (n = 3), and 9% were gender non-binary (n = 4). The baseline nightmare persistence ranged from 6 months to 13.5 years. The treatment adapted exposure, relaxation, and rescription therapy for trauma-related nightmares in adults and added elements of cognitive behavioral therapy for insomnia in children. Psychoeducation included topics of sleep and nightmares, relaxation, anxiety management, and sleep hygiene; the youth were guided through nightmare exposure and rescription.ResultsThere was a statistically significant improvement in the number of nights with awakening (Cohen's d = 1.08), the number of weekly nightmares (Cohen's d = 0.82), and nightmare distress (Cohen's d = 1.05) for the treatment group compared to the wait-list group. Parent-reported youth sleep improved for the entire group from pretreatment to posttreatment (p < 0.001) but did not reach statistical significance for between-subjects analyses of the treatment group compared to the wait-list group (p = 0.05). Between-subjects analyses saw improvement for the treatment group compared to the wait-list group on internalizing and externalizing problems and suicidal thoughts and behaviors.DiscussionThis study supports the efficacy of CBT-NC for improving sleep maintenance, nightmare frequency and distress, and other mental health difficulties in youth. Preliminary evidence of possibly improving suicidal thinking and behavior is also presented.Clinical trial registrationhttps://clinicaltrials.gov/study/NCT05588739, identifier: NCT05588739.