Introduction and objective : Botulinum Toxin-A (BTX-A) is emerging as an effective second-line treatment for idiopathic detrusor overactivity (IDO). However, little is known on its longer term effects. To further validate its use, we objectively assessed the efficacy of repeated intra-detrusor injections of BTX-A in patients with IDO. Methods : 16 patients with proven IDO received repeated BTX-A injections (range 2–4, total number of injections 45). Outcome was assessed using urodynamics, voiding diaries and validated quality of life questionnaires (IIQ-7 and UDI-6) at presentation and then at 4, 12 and 24 weeks after each injection. Data were compared between the first and the last injections. Results : The mean number of weeks between the 1st and 2nd, 2nd and 3rd, and 3rd and 4th injections was 57.0, 52.3 and 33.3, respectively. After both the first and the last injections there were significant improvements in urodynamic, IIQ-7, UDI-6 and OAB symptoms compared to baseline. No significant difference was found when comparing the data 12 weeks following the first and last injection for mean cystometric capacity ( p =0.98), reflex detrusor volume ( p =0.55), detrusor compliance ( p =0.065), maximum detrusor pressure ( p =0.9), frequency ( p =0.38), urgency ( p =0.41), urge urinary incontinence ( p =0.1), UDI6 ( p =0.7) and IIQ7 ( p =0.7). Conclusion : BTX-A appears to have a sustained efficacy following repeated administration in patients with IDO. All the authors are investigators for Allegan.