Background: Anticholinergic drugs are known to produce or enhance cognitive deficits. Tolterodine tartrate is marketed as a bladder-selective anticholinergic drug that is reported to be free of significant cognitive adverse effects. Objective: To describe a 46-year-old woman who had memory loss and abnormal memory test results that improved when she discontinued tolterodine therapy. Results: While taking tolterodine, the patient's score on the delayed free recall portion of the Hopkins Verbal Learning Test-Revised was at the first percentile. One month after discontinuing tolterodine therapy, this test was administered a second time using an alternative form and she showed marked improvement scoring above the 75th percentile. Conclusions: Tolterodine therapy caused cognitive dysfunction in our patient. It is possible that cognitive dysfunction is a common result of tolterodine treatment, but in the absence of testing, remains undiagnosed. Alternatively, our patient may have had aberrant metabolism of this drug or an increased sensitivity as a result of incipient Alzheimer disease.