Matsuzawa M, et al. - This retrospective study was undertaken to determine if seasonal climatic conditions had an impact on the onset of retinal vein occlusion (RVO) in Japan. Between April 2013 and March 2017, patients with RVO who were treated at the Juntendo University Urayasu Hospital were included. Using a chi-squared test, the frequency of occurrence of RVO across seasons was compared. A total of 348 patients [167 males and 181 females; mean age of 64.0 years (range 17–96 years)] presented with RVO during the period of study, with information about the date of RVO onset. RVO's seasonal onset tended to be higher over January/February and May/June, and lower over July/August. Such results indicate that, regardless of the patient's sex, age or hypertension status, eye care professionals should be more diligent in watching for the incidence of RVO during winter and rainy season.