The present study investigated the prevalence and heritability of nightmares and their comorbidity with psychopathology in a sample (N = 1,318) of children, adolescents, and child and adolescent twins ranging in age from 4 to 17 years old. The prevalence of terrible nightmares was estimated to be 6.4%, which is similar to previous studies. There were marginal gender differences in this rate (7.7% for boys; 5.1% in girls), contrary to previous studies that purport higher rates for girls. There was little evidence for prevalence changes across age. Nightmares were highly heritable and attributed to an additive genetic influence (51%) and nonshared environmental effects (49%). There was little evidence for a shared genetic correlation for nightmares and generalized waking anxiety (Overanxious Disorder of Childhood). There was also a substantial and pervasive comorbid psychopathology for those parents who reported Strongly True on Item 59: My child has terrible nightmares on the 200-item parent-as-respondent, Coolidge Personality and Neuropsychological Inventory. Issues in estimating prevalence rates of nightmares were identified.

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