A man in his 40s with a past history of neutropenia during zonisamide administration developed agranulocytosis 1 month after adding on topiramate to treat intractable partial epilepsy. His concurrent medication included phenytoin and acetazolamide. His white blood cell count recovered 5 days after discontinuation of topiramate. Topiramate is a sulfamate whose mechanism of antiepileptic activity is considered to include inhibition of carbonic anhydrase. Topiramate has a potential risk for haematopoietic adverse events; such events are rare and are related to immuno-allergic reaction or toxic effect of sulfonamides and sulfamates, including carbonic anhydrase inhibitors. Because this class of drugs is commonly used as an anti-glaucoma or diuretic agent, particular attention should be paid when initiating topiramate to a patient with a history of sulfonamide or sulfamate induced agranulocytosis, or when co-administrating topiramate with sulfonamides and sulfamates including carbonic anhydrase inhibitors.