A 20-year-old woman presented with an apparent acute dystonic reaction after only five doses of cimetidine (Tagamet). The patient was on no other medications with the exception of oral contraceptives. Emergency administration of IV diphenhydramine HCL brought rapid reversal of this acute dystonic reaction without any neurological sequelae. To our knowledge, this is the first reported case of an acute dystonic reaction associated with cimetidine.