PURPOSE: To investigate the efficacy and safety of repeated botulinum toxin type-A (BTX-A) injections for patients with drug-refractory nonneurogenic overactive bladder (NNOAB) and explore factors predictive of outcome. METHODS: Data were collected from all patients receiving repeated BTX-A injections for drug-refractory NNOAB between 2004 and 2012. Trigone-sparing injections were administered under sedation with antibiotic prophylaxis. Patient characteristics including age, sex, preoperative urodynamics, injection number, BTX-A dose, complications, and patient global impression of improvement (PGI-I) scores were collected. Correlations between patient factors and outcomes were assessed by using Pearson's chi-square tests. RESULTS: Fifty-two patients with a mean age of 67.4 years (range, 26-93 years) received 140 BTX-A injections in total; 33 (64%), 15 (29%), and 4 patients (7%) received 2, 3 to 4, and 5 to 8 injections, respectively. Mean follow-up time was 49 months (range, 9-101 months). Nine patients developed urinary tract infection; additionally, 3 patients experienced transient urinary retention. Median PGI-I score was 2 out of 7 (interquartile range [IQR], 2). For 46 patients, the PGI-I score remained stable with the administration of each injection. Pearson chi-square tests revealed that male patients or reduced bladder compliance was associated with a higher (worse) PGI-I score. Median PGI-I scores for men and women were 3 (IQR, 1) and 2 (IQR, 1), respectively; additionally, median PGI-I scores for those with normal bladder compliance and those with reduced bladder compliance were 2 (IQR, 2) and 4.5 (IQR, 1), respectively. Median PGI-I scores and complication rates were the same in the older patient (≥70 years) and younger (<70 years) patient cohorts. CONCLUSIONS: Efficacy is maintained with repeated BTX-A injections. Patients including the elderly show a good degree of tolerability with a low complication rate. Male patients or reduced bladder compliance is associated with poorer outcomes.