Since some authors have considered useless a differentiation between hemicentral retinal vein occlusion (HCRVO) and hemispheric retinal vein occlusion (HSRVO), we have conducted a prospective research in order to evaluate the clinical and prognostic features of these diseases. We have followed prospectively 26 cases of HCRVO and 25 cases of HSRVO. The most important risk factors were hypertension, diabetes mellitus and glaucoma in HCRVO, and hypertension in HSRVO. In the HCRVO group 20 cases (76.9%) were of the non-ischemic type and six cases (23.1%) were ischemic-type, whereas in the HSRVO seven (28%) were non-ischemic type and 18 cases (72%) were ischemic-type. Our results demonstrate that the two retinal vein occlusions are quite different with regards to pathogenesis, clinical evolution and visual outcome and point out the necessity to achieve a precise diagnosis.