The mainstay of pharmacologic treatment of overactive bladder is anticholinergic therapy. Cholinergic blockade is efficacious in decreasing the symptoms of urgency, frequency, and urge incontinence, but also is associated with undesirable side effects such as dry mouth, blurred vision, constipation, and central nervous system side effects. The property of anticholinergic agents that has been associated with increased efficacy and tolerability is receptor specificity. The safety of anticholinergic agents has been associated with the pharmacokinetics, metabolism, protein binding, and ability to penetrate the blood brain barrier. Trospium chloride, available in Europe for more than 20 years and under review by the US Food and Drug Administration for the treatment of overactive bladder, is a quaternary amine that is minimally metabolized, not highly protein-bound, and theoretically should not cross the blood brain barrier. Some of the characteristics of this unique anticholinergic agent are reviewed in this article and the relative contributions of these factors are discussed.