Interferon (IFN) related neurotoxicity includes somnolence and confusion, fatigue, lethargy, psychiatric symptoms, conceptual disorganization, neurological deficits, cortical blindness, coma and, rarely, death. The neurologic syndromes seem to be more common in elderly patients, following intramuscular or intravenous administration, at higher doses or frequent injections of IFN-α and in primary renal cell carcinoma. The duration of the treatment was not strongly related to neurotoxicity. Computed tomography findings were non-specific and included atrophy or periventricular lucencies. Electroencephalograph studies demonstrated a generalized increase in slow wave activity which returned to normal after cessation of treatment. Behavioral and mental changes in patients treated with IFN are warning signs, and indicate the need to withdraw treatment.