Acute isoniazid (INH) intoxication is a clinicical case that is characterized by epileptic seizures, coma and metabolic asidosis triad. Especially in the conditions where sufficient history cannot be obtained, this case may be confused with encephalitis, meningoencephalitis or encephalopathy. In this article, the clinical and laboratory findings and the differential diagnosis probabilities of INH intoxication are discussed under the light of literature information because of a 19-year-old case who is presented with high fever, loss of conciousness and status epilepticus, in the ethiology of which INH intoxication was later detected.