OBJECTIVES: To carry out a cost-utility analysis comparing initial treatment of patients with overactive bladder (OAB) with solifenacin 5 mg/day versus either trospium 20mg twice a day or trospium 60 mg/day from the perspective of the German National Health Service. METHODS: A decision analytic model with a three-month cycle was developed to follow a cohort of OAB patients treated with either solifenacin or trospium during a one-year period. Costs and utilities were accumulated as patients transitioned through the four cycles in the model. Some of the solifenacin patients were titrated from 5mg to 10mg/day at 3 months. Utility values were obtained from the published literature and pad use was based on a US resource utilisation study. Adherence rates for individual treatments were derived from a UK GP database review. The change in the mean number of urgency urinary incontinence episodes/day from after 12 weeks was the main outcome measure. Baseline effectiveness values for solifenacin and trospium were calculated using the Poisson distribution. Patients who failed second-line therapy were referred for a specialist visit. Results were expressed in terms of incremental cost-utility ratios. RESULTS: Total annual costs for solifenacin, trospium 20mg and trospium 60mg were 982.28 €, 863.23 € and 880.37 € respectively. Drug use represented 47%, 32% and 33% of total costs and pad use varied between 42% and 55%. Differences between cumulative utilities were small but favoured solifenacin (0.6887 vs. 0.6828 to 0.6830). The baseline incremental cost-effectiveness ratio ranged from  17,104 € to 20,533 per QALY. CONCLUSIONS: Solifenacin would appear to be cost-effective with an incremental cost-utility of no more than 21,000 €/QALY. Small differences in utility between the alternatives, however, means that the results are sensitive to adjustments in the values of the assigned utilities, effectiveness and discontinuation rates.