The term cortical blindness indicates loss of sight due to bilateral lesions in the occipital lobes. It is a rare but severe side effect produced by chemotherapeutic agents. Cortical blindness was diagnosed in a 75-year-old man who had been treated with alpha-interferon for metastatic renal-cell carcinoma. The absence of focal neurological signs and of abnormal findings as determined by two repeated computed tomography (CT) scans of the brain, which excluded structural damage to the occipital lobes, suggest that metabolic or toxic reactions may have caused the cortical blindness diagnosed in our patient. The temporal relationship between the treatment with alpha-interferon and the development of cortical blindness indicates that this substance may have been the causative agent for this phenomenon.