The present study examined the factor structure and construct validity of the Children's Loneliness Scale (CLS), a popular measure of childhood loneliness, in Belgian children. Analyses were conducted on two samples of fifth and sixth graders in Belgium, for a total of 1,069 children. A single-factor structure proved superior to alternative solutions proposed in the literature, when taking item wording into account. Construct validity was shown by substantial associations with related constructs, based on both self-reported (e.g., depressive symptoms and low social self-esteem), and peer-reported variables (e.g., victimization). Furthermore, a significant association was found between the CLS and a peer-reported measure of loneliness. Collectively, these findings provide a solid foundation for the continuing use of the CLS as a measure of childhood loneliness.