To assess the safety and efficacy of intradetrusor onabotulinum toxin A injections for the treatment of overactive bladder (OAB) in patients with Parkinson's disease (PD). All PD patients who underwent intradetrusor injections of onabotulinum toxin A (BoNT-A) for storage symptoms between 2010 and 2017 were included in a retrospective study. A 100 U dose of BoNT-A (Botox®, Allergan Irvine, CA) was used for the first injection in all patients. The primary endpoint was clinical success defined as any subjective improvement in OAB symptoms self-assessed by the patients 4 weeks after the injections. Out of 24 patients analyzed, 19 reported improvement of their OAB symptoms 4 weeks after the first injection (79.2%) with complete resolution of urgency urinary incontinence in seven patients (29.1%; P < 0.001). The average post-void residual (PVR) increased significantly after the first injection from 17.6 to 125.3 mL (P < 0.001). Three of the patients had to start clean intermittent catheterization (CIC) after the first injection (12.5%). Out of 49 injections in total, only five caused incomplete bladder emptying requiring the use of CIC (10.2%). Higher pre-injection PVR was significantly associated with both a lower chance of symptomatic improvement (P = 0.04) and a higher risk of incomplete bladder emptying with institution of CIC (P = 0.047). Intradetrusor injections of BoNT-A 100 U appeared as a safe and effective option in PD patients with OAB symptoms and a low PVR before the injection. Higher preoperative PVR was the strongest predictor of both treatment failure and postoperative urinary retention requiring CIC. © 2018 Wiley Periodicals, Inc.