Abstract : Sodium salt of valproic acid is a commonly used antiepileptic drug also used in the treatment of migraine headache prophylaxis, neuropathic pain, restless leg syndrome, dementia related agitation and social anxiety disorders. The most common adverse effects of sodium valproate are change in appetite, nausea, vomiting, diarrhea, dizziness, hair loss, gingival hyperplasia, abnormal liver function etc. Sodium valproic acid induced hyperammonemia are often seen in hepatic failure but it rarely occur with normal liver function and it is fatal. There is only less than 1% incidence rate for sodium valproate induced hyperammonemia. This is a case of sodium valproate induced hyperammonemia with normal plasma sodium valproate level (44.5mcg/ml) and with normal liver function. A 37 year old male who was admitted to the psychiatry department with reduced sleep for 4 days and anger. He had a history of Bipolar Affective Disorder, current episode mania with psychotic symptoms and Crohn’s disease. Patient was on Tablet Sodium valproate 500mg Once Daily for the past one year as a mood stabilizer. He was admitted on 11-12-2015 in the psychiatry department and continued to take Tablet Sodium valproate 250 mg Twice Daily. After few days he was found to be disoriented. Hence ammonia levels was measured on 14 -12-2015 and it was found to be 100.3umol/L (normal range 10-48umol/L). Ammonia level returned to normal after the withdrawal of the sodium valproate. He also developed gingivial hyperplasia as a side effect of the sodium valproate. This case has the causality score of 5 (hyperammonemia) and 6 (gingivial hyperplasia) using NARANJO probability scale and causality of both Adverse Drug Reactions was found to be probable. © 2017, Pharmainfo Publications. All rights reserved.