OBJECTIVES: This analysis addresses the cost-effectiveness of the extended release formulation of oxybutynin (Ditropan XL) relative to long-acting tolterodine (Detrol LA) for the treatment of overactive bladder in the US. METHODS: A previously validated state-transition model was used to compare the health economic outcomes over the course of one year using efficacy data from OPERA, a 3-month randomized, double-blind trial comparing Ditropan XL 10mg once daily to Detrol LA 4mg once daily, together with data from the literature to project outcomes beyond trial time. Five states were defined based on the severity of symptoms (number of incontinent episodes per week). Severity-specific costs (in 2003 US dollars) of pharmaceuticals, doctor visits, and pad or protection usage for incontinence in the US were used. RESULTS: Ditropan XL is expected to lead to superior outcomes and lower overall costs compared to Detrol LA. After one year, 4.6 more patients per 100 treated attain complete continence and an additional 2.4 more will have fewer than 7 incontinent episodes per week. Patients on Ditropan XL have almost 11 additional incontinence free days over the course of the year. Costs are expected to be an average of $43 lower per patient per year. Ditropan XL maintains its advantage over wide ranges of inputs, and outcomes are similar if analyses are limited to only 3 months, the duration of the OPERA trial. CONCLUSIONS: These analyses suggest that Ditropan XL provides better health outcomes and lower costs compared to Detrol LA over a one-year period.