Purpose: Our study describes the racial/ethnic composition and the broad health status/severity of disease of the cohorts of Diabetic Retinopathy Clinical Research clinical trials and compares the rates of noncompletion of the trial with the first data report (lost to follow-up). Methods: This study is a retrospective cohort study of participants in Diabetic Retinopathy Clinical Research Retina Network clinical trials who met our inclusion criteria. The primary outcome was the lost to follow-up rates and their associated risk factors. Results: Eight clinical trials with 3,492 participants met our inclusion criteria. Participants who were lost to follow-up were more likely to be younger, Hispanic or Black, had Type 1 diabetes mellitus, had worse baseline best-corrected visual acuity, had higher hemoglobin A1c, had higher blood pressure, and had proliferative diabetic retinopathy (PDR) (Diabetic Retinopathy Severity Score >66). Conclusion: Participants who were lost to follow-up during Diabetic Retinopathy Clinical Research clinical trials tended to be younger, Hispanic or Black, and had worse diabetes and hypertension. This study highlights the importance of ensuring that a representative population is maintained through the end of the study period.