The long-term effectiveness of zonisamide (ZNS) was evaluated in 11 patients with West syndrome (7 symptomatic) who had cessation of spasms with ZNS monotherapy. During the follow-up period (24 to 79 months, mean = 53 months), this response was maintained in 7 patients (3 symptomatic, relapse rate = 36%), including 2 children in whom ZNS was successfully discontinued. No serious adverse reactions were noted. ZNS may be both effective and well tolerated for the treatment of West syndrome.