Tamoxifen is a selective estrogen receptor modulator widely used in the treatment of hormone-responsive breast cancer. Tamoxifen-induced ocular complications are very rare. A post-menopausal woman with carcinoma of the left breast had presented with sudden loss of vision. The patient had been on tamoxifen therapy 20 mg daily for the last three years. Fundus examination showed left branch retinal vein occlusion. Fluorescein angiography and optical coherence tomography confirmed the diagnosis. Tamoxifen therapy was discontinued. Although branch retinal vein occlusion is rare, careful evaluation of patients on tamoxifen therapy with visual symptoms is required.