Abstract Background Tamoxifen is used to improve oncologic outcomes in a hormone receptor-positive breast cancer. High-dose tamoxifen induced ocular toxicities, and regular dose of tamoxifen is known to increase the risk of cataracts in landmark studies. The current study’s objective is to review the incidence of cataracts in ductal carcinoma in situ (DCIS) patients who received adjuvant tamoxifen treatment, which can exclude the effect of other treatment modalities such as chemotherapy and target therapy. Method Data were obtained from the National Health Insurance claims database of the Health Insurance Review and Assessment Service in South Korea. Patients diagnosed with DCIS were sorted and retrospectively reviewed for the incidence of cataracts. The primary study outcome was the incidence of cataracts according to tamoxifen, and the incidence of cataracts was defined by concomitant diagnostic and behavioral code based on International Code of Disease, 10th revision. Results A total of 12,032 patients diagnosed with DCIS and received breast surgery from 2009 to 2015 were cut down to 4,759 patients, excluding those who already had cataracts, malignancies, or had developed cataracts within a year of breast cancer surgery. There were 3,037 patients who received tamoxifen and 1,722 patients who did not, median age of 49 years old. The incidence of cataracts was similar according to the use of tamoxifen, 7.6% and 7.7% respectively. The risk of developing cataracts did not increase with or without tamoxifen, even in the group who received adjuvant tamoxifen for more than two years (HR 0.978, 95% CI 0.782-1.222, p=0.843). The findings were consistent after propensity score matching (HR 1.072, 95% CI 0.829-1.388, p=0.595). Conclusions In a nationwide cohort study, the risk of cataracts in DCIS patients is similar whether the tamoxifen is used or not. Citation Format: Dooreh Kim, Woo-Chan Park, Soyoung Jeon, Hye Sun Lee, Chang Ik Yoon. Association between tamoxifen and the incidence of cataract in ductal carcinoma in situ patients [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-03-16.