Abstract only 10569 Background: Childhood cancer survivors have excess risk of second malignant neoplasms, but data are limited in Asian populations. We established a nationwide retrospective cohort of childhood cancer survivors in Taiwan to study the risk of second malignant neoplasms in the population. Methods: Children and adolescents diagnosed with cancer before age 21 years between 1990 and 2011 were identified from the Taiwan Cancer Registry, the national cancer registry in Taiwan. One-year survivors of childhood cancer were ascertained through data linkage with the national death registry. Survivors were followed up through December 2012. Standardized incidence ratios (SIRs), absolute excess risks (AERs), and cumulative incidence of second malignant neoplasms were calculated. Results: A total of 186 second malignant neoplasms occurred among 15,263 1-year survivors of childhood cancer after a mean follow-up time of 8.0 years (SIR = 5.4, 95% confidence interval CI = 4.6-6.2; AER = 12.4 per 10,000 person-years). The most common types of second malignant neoplasms were gastrointestinal cancers (n = 37), leukemia (n = 28), endocrine cancers (n = 18), and brain cancer (n = 17). Cancers in the liver (n = 11, including 9 hepatocellular carcinoma) and colorectum (n = 16) accounted for 73% of second gastrointestinal malignant neoplasms in this population. The cumulative incidence of second malignant neoplasms at 10 and 20 years from follow-up was 1.0% (95% CI = 0.8-1.2%) and 3.0% (95% CI = 2.3-3.6%), respectively. Conclusions: Childhood cancer survivors in Taiwan experience excess risk of second malignant neoplasms, in particular gastrointestinal cancers, compared with the general population.