ENThe tremendous growth of internet use during past few decades has been primarily led by young people. Despite a plenitude of studies reporting the pros and cons of excessive internet use by adolescents, the internet use of primary school-aged children is under-researched. First, there is lack of reliable and valid cultural invariant self-report instruments for children younger than 11-years-old. Secondly, there is no consensus on whether primary school-aged children can reliably report on their internet use. This study aimed to examine the psychometric properties of the Compulsive Internet Use Scale (CIUS) as reported by primary school-aged children in three different countries/regions. Methods: Paper-pencil format CIUS questionnaires were completed by a total of 691 children aged 8 to 10 years old, 236 of them Latvian, 207 Lithuanian, and 248 Taiwanese, as well as by one of their parents, at two-time points, separated by a one-year interval. The parents also reported on the child’s emotional and behavioral difficulties. Result: Confirmatory factor analysis indicated that for the child self-report, a 10- item CIUS showed the best fit and good psychometric properties: solid structural validity; very good internal consistency; appropriate stability and predictive validity after 1 year; as well as sound sensitivity and specificity when compared to the 14-item CIUS parent-report form. Child self-report CIUS ratings correlated with time online reported by the child and parent and with emotional and behavioral problems reported by the parent. Discussion: This study indicates that children as young as 8–10 years old can reliably and consistently provide valuable information on their problematic use of the internet. Keywords: CIUS, internet use, children, multiple informants, psychometric validation. [From the publication]