Background: Research on the impact of stigma associated with mental illness in children is scarce. Considering the known negative effects of stigma associated with mental illness in adults, it is crucial to explore the stigma experienced by children who access mental health treatment. However, no scale measuring self-stigmatization in younger children is available to date. This study aimed to develop and validate such a scale, the Paediatric Self-Stigmatization Scale (PaedS). Methods: A total of 156 children (119 receiving outpatient and 37 receiving inpatient treatment), aged 8-12 years, completed the PaedS, the Self-Perception Profile for Children and the Pediatric Quality of Life Inventory (PedsQL-Child Report, ages 8-12). In addition, parents completed the PedsQL (Parent Report for Children, ages 8-12), the Strengths and Difficulties Questionnaire (SDQ) and a modified subscale of the PaedS measuring the children’s rejection by others due to their mental health difficulties. Results: A confirmatory factor analysis showed that a four-factor structure, comprising Societal Devaluation, Personal Rejection, Self-Stigma and Secrecy scales, had excellent fit to the data (CFI = 0.95; TLI = 0.95; RMSEA = 0.05). Child-reported PaedS scores were positively correlated with parental-reported PaedS scores and negatively with PedsQL, the SDQ, and 5 out of 6 subscales of the Self-Perception Profile for Children, suggesting adequate convergent validity (all P-values < 0.05). Conclusions: The PaedS is a valid instrument, which is hoped to advance the understanding of self-stigmatization in children with mental health difficulties and contribute to its prevention.