Abstract Background: Weight management is now included in the American Cancer Society/American Society of Clinical Oncology Breast Cancer Survivorship Care Guidelines due to its clinical impact on breast cancer (BC) survivorship outcomes. While numerous individual-level risk factors for weight gain after BC diagnosis have been identified, such as younger age at diagnosis, cancer stage, and cancer treatments (chemotherapy), there are limited data on the impact of neighborhood-level factors associated with weight change postdiagnosis among Black BC survivors. Methods: Utilizing social media recruitment strategies and survivor networks, we recruited 100 Black female BC survivors to complete an online survey, including demographic, clinical characteristics, and lifestyle factors, between January 5, 2022, and August 18, 2022. To capture the food environment, we utilized the 2023 Food Environment Index County Health Rankings, which accounts for access to healthy foods due to proximity and income (considering the distance an individual lives from a grocery store or supermarket, locations for health food purchases in most communities, and the inability to access healthy food because of cost barriers). The index ranges from 0 (worst) to 10 (best). Our outcome of postdiagnosis weight gain was calculated as percent weight change from time at diagnosis to time of survey, calculated as ([weight at survey – weight at diagnosis]/weight at diagnosis) × 100. Participants were grouped into mutually exclusive categories of stable weight (within ± 3%) or weight loss (≤-3%) compared to weight gain (≥ 3%). Adjusted odds ratios (aORs) and 95% confidence intervals (CI) were calculated for the associations between clinical factors, county-level food environment index, and postdiagnosis weight gain. Results: The average ages at time of survey and at primary BC diagnosis were 58.6 years (standard deviation [SD]= 10.1) and 49.1 years (SD=10.2), respectively. Most women (70%) were diagnosed with invasive BC and only 22% were currently undergoing treatment at the time of the survey. While only 7% reported being obese at the time of BC diagnosis, 54% reported being obese at the time of survey which was on average 9 years post-BC diagnosis; and while 61 women had weight loss or stable weight, 34 women experienced weight gain postdiagnosis. Among the 95 women included in multivariable models who reported weight and height measurements for calculating weight change, women ≥50 years of age at BC diagnosis (versus < 50 years) were 3.43 times more likely to gain weight after diagnosis (95% CI 1.13-11.50). Women living in counties with a Food Environment Index ≥8.8 (median cut-point compared to < 8.8) were significantly less likely to experience weight gain (aOR 0.11; 95% CI 0.01-0.90). Stage and BC treatments were not significantly associated with weight gain. Conclusions: Our study findings demonstrate the importance of evaluating the food environment during BC survivorship and longitudinal monitoring of weight postdiagnosis to mitigate weight gain among Black BC survivors. Our findings will be used to inform a larger prospective study and future interventions among this population. Citation Format: Avonne Connor, Katherine Ho, Kate Dibble, Kala Visvanathan. Age at diagnosis and the food environment are associated with postdiagnosis weight gain among Black American breast cancer survivors in Maryland [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 PO3-27-07.