Abstract Background and Purpose: Mailed fecal immunochemical testing (FIT) is an evidence-based strategy to increase colorectal cancer (CRC) screening. We have previously reported that a multi-level mailed FIT intervention resulted in higher CRC screening rates compared to usual care among Hispanic patients receiving care at Community Health Centers (CHCs). The objective of this study was to assess predictors of mailed FIT completion among Hispanic individuals. Methods: The San Diego Accelerating Colorectal Cancer Screening and Follow-up through Implementation Science (ACCSIS) project tested a multi-level mailed FIT intervention in 3 CHC systems in Southern California. Using a cluster-randomized trial design, 9 clinics were randomized to mailed FIT and 16 to usual care. The intervention was delivered in Spanish and English and included an invitation letter, a mailed FIT kit with completion instructions, and phone and text-based reminders. Multi-level implementation strategies (i.e., training, centralized facilitation, etc.) were utilized to increase uptake. For this analysis, we assessed mailed FIT completion at 1 year among Hispanic participants ages 50-75 years not up-to-date with CRC screening at baseline and who were randomized to clinics in the mailed FIT intervention. We conducted logistic regression to assess relationships between sex, language preference, health insurance and mailed FIT return. Results: Among the 9 intervention clinics, 2,199 Hispanic patients who were age-eligible and not up-to-date with CRC screening at baseline were included in the present analysis. In this group, 1,457 (66.3%) were female, 1,449 (65.9%) were Spanish-speaking, and 769 (35.0%) returned the FIT kit. Variation in FIT return for Hispanic individuals was shown across CHC systems: 53.2% in CHC1, 31.4% in CHC2, and 24.7% in CHC3. The percentage of individuals who returned the mailed FIT was highest among 55 to 59-year-olds (39.4%) and lowest among 50 to 54-year-olds (30.6%). Results from univariate logistic regression showed that individuals who preferred Spanish language had higher return rate than those who preferred English (OR=1.44; 95% CI: 1.17-1.77). FIT return was higher among participants who were privately insured compared with Medicaid-insured individuals (OR=1.57; 95% CI: 1.20-2.06). Return rate was higher among females compared to males, but the difference was not statistically significant (OR=1.13, 95% CI: 0.98-1.29). Conclusions: Among Hispanic patients who receive care at CHCs, a regional mailed FIT intervention was effective at increasing screening rates. Mailed FIT completion among participants randomized to clinics in the intervention group varied by language preference and health insurance status. These results suggest that future efforts could be tailored to increase FIT return rates among English-speaking Hispanics and those with Medicaid insurance. Citation Format: Joshua Demb, Maria Elena Martinez, Scott Roesch, Samir Gupta, Valesca Largaespada, Sheila F. Castañeda, Borsika A. Rabin, Jennifer Covin, Kristine Ortwine, Yesenia Preciado-Hidalgo, Nicole Howard, James Schultz, Nannette Stamm, Daniel Ramirez, Michael T. Halpern, Jesse Nodora. Predictors of mailed fecal immunochemical test return for Hispanic patients receiving care at community health centers [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr A122.