Fluoxetine and other selective serotonin reuptake inhibitors (SSRIs) are effective for the treatment of depression in the elderly and offer a safer side-effect profile as compared to tricyclics and monoamine oxidase inhibitors. We report a case in which a patient treated with fluoxetine developed parkinsonism following the introduction of cimetidine. Inhibition of hepatic P450 cytochrome enzymes by cimetidine with an increase in serum levels of norfluoxetine may have precipitated this extrapyramidal syndrome, which has been related to agonism of the serotonergic input to nigrostriatal tracts and basal ganglia. Parkinsonism as a side effect of SSRIs occurs infrequently, suggesting an idiosyncratic response resulting from a functional imbalance of serotonergic and dopaminergic activity in susceptible individuals. Careful monitoring of geriatric patients treated with fluoxetine is indicated, particularly for those on high doses, those with impaired hepatic functioning, or those treated with concurrent medications that slow the metabolism of fluoxetine.