Abstract Background: Post-mastectomy immediate breast reconstruction (PMIBR) has been underutilized in the elderly. This study examines the trends of PMIBR by age in a large Korean medical center and compares them to the Asian-American population in the National Cancer Database (NCDB). Methods: We analyzed 5,601 patients who underwent PMIBR out of 13,654 total mastectomy patients between 2001 and 2021 in a Korean Center. Patient characteristics associated with higher likelihood of receiving reconstruction were assessed and compared between patients under 60 years of age and those aged 60 years and older. Complications were investigated in 1,669 patients between 2010 and 2020. In addition, we compared this to 966,354 female patients in the NCDB from 2004-2020 with stage 0-3 breast cancer who underwent mastectomy. Results: The number of PMIBR at the Korean center increased almost ten-fold, but there was a discrepancy in the increase between younger and older women. In the younger group, the proportion of PMIBR rose from 13% (53/398) to 77% (508/664), while in the older group, it increased from 0% (0/60) to 26% (49/186). In the NCDB, Asian-Americans had the lowest rate of breast reconstruction (29%) compared to white (35.4%), black (30.1%), and Hispanic Americans (33.5%). As seen in the table, the rates increased in both age groups but plateaued around 2014 and remained stable until 2020. In 2020, the PMIBR rates were 37% for young Asian-Americans, 48% for young non-Asians, 14% for older Asian-Americans, and 24% for older non-Asians. At the Korean center, patients living in a metropolitan area (42.6% vs.39.8% p=0.001), having higher education (44.7% vs. 10.5% p< 0.001), being unmarried (63.1% vs. 39.3% p< 0.001), having no history of childbirth (53.7% vs 39.9% p< 0.001), having lower stage and hormone receptor-positive HER2-negative breast cancer were more likely to undergo reconstruction. These factors were all more common in the younger age group. In the NCDB, patients receiving PMIBR were more likely to be white or non-Asian, have higher income and education, reside in a metropolitan area and in the Northeast, have less comorbidities, be treated in an academic center, and have a luminal subtype, lower stage, and private health insurance. At the Korean center, autologous reconstruction was more common than implant reconstruction, (68.4% vs. 31.6% for younger women, and 63.3% vs. 36.9% for older women) and the complication rate was similar for both age groups. In contrast, in the NCDB, implant reconstruction was more common in both age groups, tissue-based (29% vs 31%), implant-based (40.7% vs 40%), combined (11% vs 10.8%) and other (18% vs 17.6%) for older and younger women respectively. Conclusion: Both the Korean and American data illustrate remarkably lower utilization of immediate breast reconstruction in older patients. There are notable demographic and clinical differences between age groups but negligible difference in complication rates. Further research and interventions to address barriers in older women are needed. The higher rates of PMIBR in South Korea mirrors that of white women in the northeast USA, suggesting a potential disparity for Asian-Americans. Percentage of PMIBR over total mastectomy (with or without reconstruction) by age and race PMIBR= post-mastecomy immediate breast reconstruction; NCDB= national cancer database Citation Format: Soo-Young Lee, Madhav KC, Hyun Ho Han, Leah Kim, Mehra Golshan, Eric Schneider, Rachel Greenup, Donald Lannin, Hyung Bae Kim, Byung Ho Son, Jong Won Lee, Sae Byul Lee, Hee Jeong Kim, Tristen Park. Trends in post-mastectomy reconstruction by age in Korea and among Asian-Americans [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-17-11.