Phenytoin is an anticonvulsant and Hydantoin, it is mainly used in the management of Seizures, and it stabilizes the neuronal membranes and decreases seizure activity by increasing ef lux or reducing the in lux of sodium ions across cell membranes in the motor cortex during the generation of nerve impulses. It is available in the market in the form of oral and intravenous forms, a loading dose of Phenytoin for the management of seizures is 10-20 mg, divided into 2-3 doses. Stevens-Johnson syndrome is a rare and serious adverse effect of the skin along with the membranes of the mucous. It is caused by speci ic Drugs or Viral Infections. We have performed causality assessment by using the WHO and NARANJO'S ADR rating scale. It will seem, it is a Probable ADR, and severity assessed it confers a Type-A ADR, and it should be in Probably Preventable. So being a Reliable Clinical Pharmacist, we recommend to all health care professionals be aware of adverse drug reactions, and Desirable vigilance is necessitated toward safe and effective management for speci ic patients, strictly observe the patients in sequence anticipate Dangerous Adverse events.