Aims: Despite the efficacy of intravesical onabotulinumtoxinA (Botox) therapy for urgency, urgency incontinence, and daytime frequency, its value in treatment of nocturia remains unclear. The aim of the prospective observational study was to assess the effect of onabotulinumtoxinA on night-time symptoms in women with overactive bladder (OAB), including nocturia, night-time urgency incontinence, and nocturnal voided volume as end-points. Methods: Women with idiopathic OAB (with at least one episode of urgency urinary incontinence (UUI) per day, 8 micturitions per 24hr, and 2 nocturia episodes per night) were enrolled. Patients with nocturnal polyuria were excluded. Botox (100U) was administered in 20 intra-detrusor injections. Post-void residual volumes (PVR) were checked at 2, 4, and 12weeks. Participants completed a 3-day bladder diary and the King's Health Questionnaire (KHQ) before and 12 weeks after treatment, and reported the efficacy of the treatment on visual analog scale (VAS) at the final follow-up visit. Results: Seventy-six women completed the study. Botox injections were effective in the reduction of nocturia episodes (mean -0.98; P<0.001) and night-time UUI episodes (-0.37; P<0.001) compared to the baseline. The increase of mean voided volume of the night-time micturitions was 92.6ml (P<0.001). Patients reported a mean 58 points of improvement on the VAS. Urinary retention, which required self-catheterization, was observed in three patients. Conclusions: Intravesical Botox injection provides significant benefit for night-time symptoms in OAB patients. Our results are applicable for women without nocturnal polyuria, and should prove useful when counseling patients about the risks and benefits of Botox. Neurourol. Urodynam. 36:648-652, 2017. (c) 2016 Wiley Periodicals, Inc.