RADIANT is an NIH study of people with uncharacterized forms of atypical diabetes mellitus (DM) in the US. RADIANT participants consent online and progress through three sequential stages of study procedures, as eligible. DM in underrepresented minorities (URM) is rapidly increasing in incidence and has worse outcomes than DM in non-Hispanic whites. RADIANT pre-set targets proportionate to ethnic/racial distribution in the US to enroll individuals from a wide racial/ethnic spectrum. We aimed to study the URM participation in RADIANT across study stages. Enrollment rate for URM was significantly below pre-set targets at consent and across most stages (Table 1) . Referral sources significantly differed by races (p=0.003) but not ethnicities (p=0.16) . Most African-Americans (54%) were referred by RADIANT investigators but flyers, news, social media and family or friend were the major sources of referral for whites (30%) . Some of the initiatives to increase URM in RADIANT include engaging with clinics serving URM, working with local clinics/hospitals, electronic medical record screening approaches, increased focus on DM types more frequent in URM, providing culturally competent study coordination and targeted advertisement. In sum, enrollment rate of URM in RADIANT is suboptimal. Investigating barriers and facilitators for minority recruitment in RADIANT, with implications for other studies, is warranted. Disclosure M. Tosur: Advisory Panel; Provention Bio, Inc. A. Balasubramanyam: None. R.N. Naylor: None. T.I. Pollin: Research Support; Regeneron Genetics Center, Regeneron Pharmaceuticals Inc. N. Rasouli: Advisory Panel; Eli Lilly and Company, Novo Nordisk, Sanofi. Research Support; Allergan, Eli Lilly and Company, Novo Nordisk. J.B. Buse: Consultant; Alkahest, Anji, AstraZeneca, Boehringer Ingelheim International GmbH, Cirius Therapeutics, Inc., Eli Lilly and Company, Fortress biotech, GentiBio, Glycadia, Glyscend, Janssen Pharmaceuticals, Inc., Mellitus Health, Moderna, Inc., Pendulum Therapeutics, Praetego, LLC, Stability Health, Valo, Zealand Pharma A/S. Research Support; AstraZeneca, Dexcom, Inc., Eli Lilly and Company, Novo Nordisk, vTv Therapeutics. Stock/Shareholder; Glyscend, Mellitus Health, Pendulum Therapeutics, PhaseBio Pharmaceuticals, Inc., Praetego, LLC, Stability Health. Other Relationship; Adocia, AstraZeneca, Eli Lilly and Company, Intarcia Therapeutics, Inc., MannKind Corporation, Novo Nordisk, Sanofi, Senseonics, vTv Therapeutics. M.J. Redondo: Advisory Panel; Provention Bio, Inc. Funding National Institutes of Health (U54, DK118638-01)