Purpose: This study determined the clinical impact and causes of loss to follow-up (LTFU) from the patients’ perspective in individuals with proliferative diabetic retinopathy (PDR) who received panretinal photocoagulation (PRP) and/or intravitreal injections (IVIs) of anti-vascular endothelial growth factor (VEGF). Methods: This prospective cohort study included 467 patients with PDR who received PRP and/or IVIs of anti-VEGF between May 2013 and June 2018. LTFU was defined as missing any follow-up visit for any interval exceeding 6 months, provided that patients eventually resumed care. Main outcome measures include rates and causes of LTFU. Results: A total of 391 patients (83.7%) were followed, and 76 patients (16.3%) were LTFU over the study period. Rates of LTFU decreased with age (P = 0.005). Questionnaire analysis conducted for patients LTFU showed a significant positive correlation between best corrected visual activity (BCVA) loss and patient’s lack of trust and satisfaction with treatment [rs = 0.458, P 0.001]. There was also a significant positive correlation between treatment unaffordability and number of IVIs of anti-VEGF [rs = 0.55, P 0.001] and lack of social support and age [rs = 0.39, P 0.001]. Conclusions: LTFU threatens vision in PDR patients receiving PRP and/or IVIs of anti-VEGF. Possibly, patient-specific LTFU causes should be addressed before treatment in order to minimize the risk of LTFU.