Nonsteroidal antiinflammatory drugs (NSAIDs) have arterial vasospastic properties. The authors report a stroke that occurred within minutes following an intramuscular injection of diclofenac. A sixty-one-year-old man, a heavy smoker, was admitted for an acute onset of mild hemiparesis thirty minutes after a single intramuscular injection of diclofenac. The neurologic deficit was resolved at one month of follow-up. The authors suggest a temporal causal relationship between the cerebrovascular event and the injection of diclofenac. The mechanism of stroke might be related to a synergistic vasospastic property shared by the use of an NSAID and heavy smoking.