Purpose: Adolescent and young adult (AYA, 15-39 years) cancer survivors (alive at least 5 years after cancer diagnosis) are less studied than younger and older cancer survivors and research on their late effects is limited. To facilitate research on long-term outcomes of AYA cancer survivors, we established, in Italy, a population-based AYA cancer survivors' cohort. This article describes the study design and main characteristics of this cohort. Methods: The cohort derives from population-based cancer registries (CRs). Each CR identified AYA cancer patients retrospectively. Treatment for first primary cancer and all health events from diagnosis to death can be traced through linkage with available health databases, such as hospital discharge records (HDRs), mortality files, and outpatient and pharmaceutical databases. Results: Thirty-four CRs participated to the cohort which overall includes 93,291 AYAs with cancer and 67,692 cancer survivors. First primary cancer distribution in AYA cancer survivors differs by sex and age groups because of the different cancer types diagnosed in AYAs. Almost 78% of AYA cancer survivors have HDRs and 14.8% also pharmaceutical and outpatient databases. Conclusion: This cohort will be used to study, for the first time in Italy, the pattern and excess risk of late effects in AYA cancer survivors. HDRs, outpatient and pharmaceutical databases will be used to define primary treatment to assess its impact on AYA cancer survivors' late effects. This cohort exploiting data sources already available at CRs, minimize the data collection effort and it will contribute to assess the feasibility of using administrative database to study cancer survivors' late effects.