Introduction:Colorectal cancer is a leading cause of cancer-related mortality in the United States. Current screening recommendations for individuals aged 50 to 75 years include colonoscopy every 10 years, flexible sigmoidoscopy every 5 years, or annual stool-based testing. Stool-based testing, including fecal immunochemical tests (FITs), are cost effective, easy to perform at home, and noninvasive, yet many patients fail to return testing kits and go unscreened. The purpose of the study was to identify patient characteristics and perceived barriers and facilitators of FIT return.Methods: Patients in a large, federally qualified health center who received a FIT kit order between January 1 and July 1, 2017 were identified. We compared sociodemographic and health characteristics between patients who returned and did not return FITs. We used telephone surveys to nonreturners to identify potential barriers (cost, knowledge, psychosocial factors) and facilitators (prepaid postage, outreach) of FIT kit return. An online survey of clinicians assessed perceived patient barriers and facilitators of colorectal cancer screening.Results: Of the 875 patients who received a FIT order, 435 (49.7%) did not return the kit and 121 of the nonreturners completed a telephone survey. Current smokers had an increased risk of FIT nonreturn compared with never smokers (RR ‫؍‬ 1.32; 95% CI, 1.13-1.54). Forgetfulness and lack of motivation were the most common FIT return barriers perceived by both patients and clinicians. Prepaid postage with return address on FIT return envelopes and live call reminders were the most commonly reported facilitators. Barriers and facilitators varied greatest between English-and Spanish-speaking patients.Conclusion: In this study, the most common perceived barriers to return of screening fecal test kits were forgetfulness and lack of motivation. The most common perceived facilitators were live call reminders and postage-paid return envelopes. Understanding barriers and facilitators to FITs may be necessary to enhance cancer screening rates in underserved patient populations. (J Am Board Fam Med 2019;32:180 -190.)Colorectal cancer is the second most common type of cancer-related death in men and the third most common in women; over 50,000 deaths a year in the United States are attributable to colorectal cancer. 1 Although substantial progress was made over the past 2 decades and colorectal cancer death rates This article was externally peer reviewed.