A 79-year old female patient with Alzheimer's disease developed acute dystonia twelve hours after taking a single dose of mirtazapine 30 mg. Forty-five hours later the patient's dystonia began to subside and after sixty hours it had disappeared completely. This side-effect of mirtazapine is hardly mentioned in the literature. So far, little is known about the pathophysiology of acute dystonia and the possible role of mirtazapine. Some hypotheses and recommendations are proposed.