Aim: To investigate the diurnal variation that is related to the incidence of branch retinal vein occlusion (BRVO). Methods: This is a cross-sectional study. 72 consecutive patients who were newly diagnosed with BRVO were precisely questioned about the time of their symptom onset. The clinical history, systemic illnesses, ocular findings, and body mass index were obtained for each patient. Results: Analysis of the diurnal variation of symptom onset showed a distribution with the peak in the period from 6 a.m. to noon compared with all the other time periods (p < 0.001). Multivariate analysis showed that involvement of the superior retina was the only factor that influenced the onset time of BRVO. Conclusion: Patients with symptomatic BRVO frequently noted their visual deterioration in the morning, which is the same as the other types of ocular and systemic vascular disease. Our results may be helpful for understanding the pathophysiology of BRVO. Our findings require conformation and further studies on this subject are certainly warranted.