OBJECTIVES: To compare the estimated first-line treatment costs of extended-release tolterodine versus controlled-release oxybutynin in patients with overactive bladder patients (OAB). METHODS: Data from a randomized clinical trial (Curr Med Res Opin 2002;18:177-184), showing greater improvement in bladder condition for patients taking extended-release tolterodine compared to controlled-release oxybutynin (70% vs. 60% in all patients, 75% vs. 54% in patients with prior therapy, and 69% vs. 61% in treatment naïve patients), was used to conduct the analyses. The analysis input trial outcomes into an existing decision analysis model that had shown extended-release tolterodine was 6.3% less expensive than controlled-release oxybutynin in terms of the cost of treatment. Analyses were constructed from the payer perspective; all costs are given in 2000 U.S. dollars. RESULTS: The decision analysis model yielded results that ranged between a 5.7% and 7.0% total cost of treatment advantage for extended-release tolterodine in the treatment of all patients. This cost advantage was 5.1%-6.3% for treatment-naïve patients and 8.9%-10.8% for previously treated patients. The variation in the results depended on the model timeframe chosen (12, 14, or 16 weeks). Sensitivity analyses showed these results to be stable. CONCLUSIONS: Results from these analyses confirm earlier studies that, for patients with OAB and initiating long-acting pharmacologic therapy in the primary care setting, treatment with extended-release tolterodine is less costly than treatment with controlled-release oxybutynin. Additional studies directly comparing these treatment alternatives are needed to further confirm these results.