Exudative retinal detachment (ERD) is an uncommon complication of branch retinal vein occlusion (BRVO). The ERD pathogenesis has been mainly related to the haemodynamic overload and to an impairment in the function of the retinal pigment epithelium. Data relative to 98 cases of BRVO without ERD were compared with the correspondent data of 10 cases of BRVO with ERD. Venous leakage showed a substantial equivalency between the two groups, while evaluation of retinal venous collaterals demonstrated a lower amount in the BRVO cases with ERD, with a statistically significant difference. Moreover, considering the various ERD localizations, we suggest that the ERD pathogenesis is mainly ascribable to the scant development of retinal venous collaterals but that an important role may also be played by the retinal pigment epithelium impairment consequent to the retinal ischaemia.