OBJECTIVES Treatment options for patients for whom urinary incontinence (UI) due to idiopathic overactive bladder (OAB) is inadequately managed by anticholinergic therapy are limited, and can be expensive, invasive and inefficacious. This can lead to a significant economic burden to hospitals and healthcare systems.  OnabotulinumtoxinA may provide an effective and minimally-invasive treatment option for OAB.  An economic model was developed to investigate potential cost savings associated with the use of OnabotulinumtoxinA – as an adjunct to best-supportive care (BSC) – to manage OAB rather than other treatment options in Spain. METHODS A prevalence-based, deterministic budget impact model with a five-year time horizon was developed from the perspective of the Spanish healthcare system.  The model took into account the cost of drugs, disposables (e.g. incontinence pads) and devices, procedures, monitoring costs, and the cost of managing adverse events.  Model input data were derived from the Spanish Ministry of Health, published and unpublished clinical studies, clinical guidelines, and expert opinion. RESULTS In the Spanish population, an estimated 96,360 individuals were eligible for treatment with OnabotulinumtoxinA for OAB.  Compared to a current treatment pattern in which 5% of patients received OnabotulinumtoxinA, increasing OnabotulinumtoxinA usage annually from 10% in year 1 to 30% in year 5 resulted in an estimated cost saving of €26.4 million over five years.  This saving represented a 4.7% decrease in overall spending compared to the current treatment pattern.  Increased drug acquisition costs were entirely offset by savings due to decreased use of incontinence pads and anticholinergic therapy. CONCLUSIONS Costs associated with inadequate management of UI due to OAB are significant and avoidable.  Our model estimated that managing patients with OnabotulinumtoxinA may reduce the economic burden to the Spanish healthcare system, with increased acquisition costs of OnabotulinumtoxinA completely offset by savings due to decreased resource use.