BACKGROUND: Although adolescent and young adult (AYA) cancer survivors have an increased risk of psychiatric disorders, limited evidence has been suggested. We aimed to determine the risk of psychiatric disorders among AYA cancer survivors. MATERIALS AND METHODS: A retrospective population-based cohort study based on the Korea National Health Insurance Service database was carried out. All men and women aged 15-39 years diagnosed with cancer between 2006 and 2019 (N = 88 965) were included and matched with controls (1 : 4). The prevalence ratios (PRs) of psychiatric disorders were calculated in cancer patients and compared with those in the control group every 6 months before and after cancer diagnosis. RESULTS: The mean age of the participants was 32.2 years and the majority were 30-39 years of age (72.9%). There was no difference in the PRs of psychiatric disorders between AYA cancer patients and the control group before cancer diagnosis, but it increased sharply after cancer diagnosis [PR 2.50, 95% confidence interval (CI) 2.42-2.58 in the first 6 months]. During a median follow-up of 6.5 years, 54 733 participants developed psychiatric disorders. The overall risk of psychiatric disorders among AYA cancer survivors compared with the control group had a sub-distribution hazard ratio of 1.42 (95% CI 1.39-1.45) after considering competing risks. CONCLUSIONS: Our study confirmed a 42% increased risk of psychiatric disorders among AYA cancer survivors compared with controls across various cancer types. Our findings suggest that AYA cancer survivors require long-term psychological support following their cancer diagnosis.