Depression increases dramatically during adolescence. This finding has been demonstrated using multiple measures, including the Children’s Depression Inventory (CDI). The CDI is one of the most commonly used measures to assess depression in youth. However, there is little agreement on its factor structure, and it is possible that its factor structure changes over time. Yet, no study to date has investigated whether this structure is longitudinally invariant from early- to mid-adolescence. The present study examined the factor structure of the CDI in a sample of 227 adolescents aged approximately 13 at baseline and 16 at follow-up. The analyses revealed that a one-factor structure was a good fit to the data at each assessment. Moreover, tests of measurement invariance supported configural, metric, and scalar invariance across time. These findings suggest that changes in depressive symptoms during adolescence are due to true developmental changes, rather than changes in measurement properties.