Based on the understanding of the pathophysiology of OAB and detrusor overactivity (DO), BoNT has been enthusiastically applied in treating urinary urgency or incontinence refractory to antimuscarinics in recent years. Although promising therapeutic effects have been confirmed by several case series or clinical trials, the occurrence of adverse events are reported inconsistently. Analysis of patients demographics and urodynamic variables reveals that patients with ageing, low detrusor contractility, with chronic medical disease carry risks of adverse events. Although safety and efficacy were similar between elderly patients without frailty and younger patients, an increased risk of large post-void residual urine volume and a lower long-term success rate in frail elderly patients were noted after intravesical 100 U BoNT-A injection for refractory idiopathic DO. Therefore, careful dose and injection site adjustment and patient selection is mandatory to achieve satisfactory results using intravesical BoNT-A therapy.