Background: Knowledge on the significance of childhood psychotic symptoms and experiences (PE) is still limited. This study aimed to investigate the prevalence and clinical significance of PE in preadolescent children from the general population by use of in-depth psychopathological interviews and comprehensive diagnostic assessments. Methods: We investigated 1,632 children from the general population-based Copenhagen Child Cohort 2000. PE were measured by semistructured interviews using the K-SADS-PL-items on psychotic and affective symptoms, each symptom scored as not present versus likely or definitely present. The Development and Well-Being Assessment (DAWBA) was used independently to diagnose DSM-IV-mental disorders. Puberty development and sleep disturbance were self-reported. The associations between PE (any lifetime hallucination and/or delusion) and various mental problems and disorders were examined by multivariable binomial regression analyses, adjusting for gender and onset of puberty. Results: The weighted life time prevalence of PE at age 11-12 years was 10.9% (CI 9.1-12.7). The majority of children with PE (n = 172) either had a diagnosable DSM-IV-mental disorder (31.4%) or self-reported mental health difficulties in absence of a diagnosis (31.4%). The risk of delusions increased with onset of puberty. The risk of PE increased with emotional and neurodevelopmental disorders, subthreshold depressive symptoms, sleep problems and lack of sleep, regardless of whether PE were expressed as hallucinations and/or delusions. The highest correlations were seen for emotional and multiple disorders. Conclusions: Psychotic experiences are particularly prevalent in the context of affective dysregulation and sleep disturbance, increase with onset of puberty and represent a trans-diagnostic marker of psychopathology.