A 38-year-old man presented with an acute right homonymous visual field defect due to occipital lobe infarct caused by hyperhomocysteinaemia. Visual field testing, magnetic resonance imaging, laboratory studies, and genetic analysis were carried out. On magnetic resonance imaging, a left occipital lesion with bright signal on the diffusion-weighted and fluid-attenuated inversion recovery images suggested a diagnosis of an acute infarct. Blood tests revealed raised homocysteine of 52.08 μmol/L (reference range, <15 μmol/L) and genetic analysis showed the patient to be homozygote to 5, 10-methylenetetrahydrofolate reductase deficiency. Hyperhomocysteinaemia is a rare causes of acute visual loss due to cerebral ischaemia and should always be suspected and investigated with the appropriate tests to diagnose the condition and limit further vision deterioration.