Background/aim: The aim of this study is to study subclinical platelet activation by detecting three important platelet activation parameters of mean platelet volume (MPV), platelet distribution width (PDW), and plateletcrit (PCT) in patients with branch retinal vein occlusion (BRVO) in comparison to those in healthy control subjects.Materials and methods: This prospective study included 43 patients with BRVO (Group 1)and 40 control subjects (Group 2). The levels of MPV, PDW, and PCT were measured in both of the studied groups.Results: The mean serum level of MPV value was 7.64 ± 0.64 in Group 1 and 7.39 ± 0.42 in Group 2. Mean serum level of PDW was 15.01 ± 1.56 in Group 1 and 14.43 ± 1.03 in Group 2. Mean serum PCT value was 0.19 ± 0.05 in Group 1 and 0.16 ± 0.04 in Group 2. MPV, PDW, and PCT levels were significantly increased in BRVO patients (P < 0.05).Conclusion: Subclinical platelet activation reflected by MPV, PDW, and PCT may have an impact on the genesis of vessel occlusion in BRVO. The results may be important for the clinical management of patients with BRVO.