STUDY TYPE Therapy (case series). LEVEL OF EVIDENCE 4. What's known on the subject? and What does the study add? We know that repeated injections of botulinum toxin A are effective in treating refractory detrusor overactivity particularly in NDO. This study shows that in both NDO and IDO repeated injections of the toxin improve quality of life as assessed by three validated questionnaires. The effect is most marked after the first injection in NDO patients but thereafter similar in both groups. OBJECTIVE To compare the effect of repeated detrusor injections of botulinum toxin (BoNT-A) on health-related quality of life (HRQL) in patients with idiopathic (IDO) or neurogenic detrusor overactivity (NDO). PATIENTS AND METHODS Between 2003 and 2009, 151 patients (109 with NDO and 42 with IDO) were treated by BoNT-A (Botox®, Allergan Inc., Irvine, CA, USA). Changes in HRQL were assessed using the validated short forms of Urogenital Distress Inventory (UDI-6), the Incontinence Impact Questionnaire (IIQ-7) and EuroQOL-5D (EQ-5D) before and 4 weeks after BoNT-A. RESULTS The maximum number of repeated injections was five (mean±sd, 2.8±1.05). Mean±sd follow-up was 27.49±17.01 months. The UDI-6 and IIQ-7 questionnaires showed a consistent improvement after repeated injections in both groups with detrusor overactivity. The EQ-5D was not statistically different before and after each injection in either the NDO or IDO population. After repeated injections, no statistical differences in the change on the UDI-6 and IIQ-7 scores were found between NDO and IDO, except after the first treatment, when the decrease in UDI-6 was higher in NDO than in IDO. The EQ-5D anxiety and depression subscore improved in both groups after each injection and with the number of injections. In IDO, after the second injection, no patient reported extreme anxiety or depression and, after the fourth injection, none had anxiety or depression. The inter-injection interval was shorter after the first injection in those with NDO than in IDO but was similar thereafter. CONCLUSIONS Intradetrusor injections of BoNT-A improved the HRQL of both NDO and IDO patients. Although improvement in HRQL was greater and the duration of efficacy shorter in NDO patients after the first injection, there was no significant difference after subsequent injections. Mean inter-injection interval in IDO and in NDO patients was similar from the second injection onwards and improvements in HRQL score were the same.