OBJECTIVES: Overactive bladder (OAB) is a common, chronic and distressing medical condition that affects individuals of all ages, and is associated with an increased risk of comorbidities. Tolterodine is an antimuscarinic drug indicated for the treatment of OAB, and is available as both an immediate-release (IR), twice-daily, tablet formulation of tolterodine and extended-release (ER), once-daily, capsule formulation. The aim of this analysis is to carry out an economic evaluation of IR versus ER tolterodine in the management of OAB in Spain. METHODS: A cost-effectiveness analysis was performed by building a decision analytic model. Efficacy, tolerability and healthcare resource utilization data were obtained from a double-blind, multicenter, randomized trial showing that ER formulation was more effective and better tolerated than the IR formulation 1. Only direct medical costs-drug acquisition, physician visits, diagnostic evaluations, incontinence pads and treatment of skin complications and urinary tract infection- were taken into account. Drug costs were obtained from official sources, and the rest of data were taken from a national health care cost database. The perspective selected for this analysis was primary care assistance and the time horizon was 12 weeks, the treatment period in the referenced clinical trial. RESULTS: The percentage of patients treated with ER tolterodine had a greater control on OAB symptoms (71% vs 60%, p<0.05) and a lower cost/effectiveness ratio (375 vs 414€ per patient with successful outcome) than patients treated with IR tolterodine. CONCLUSIONS: This model demonstrates that ER tolterodine is a more efficient therapeutic option than IR tolterodine despite of the difference in acquisition costs between the two formulations. Therefore, ER could be considered as the tolterodine formulation to be selected routinely in the management of OAB in Spain.