We investigated the efficacy and tolerability of solifenacin 5 mg fixed dose in children with newly diagnosed idiopathic overactive bladder (OAB). A total of 34 children (male/female patients = 16/18) aged under 13 years (mean age: 7.2 +/- 2.3; range: 5-12) who were newly diagnosed with OAB from January 2012 to September 2014 were prospectively evaluated with open-label protocol. All patients were treated with solifenacin 5 mg fixed dose once daily for at least 4 weeks. The efficacy and tolerability of solifenacin were evaluated 4, 8, and 12 weeks after the initiation of treatment. The mean voiding frequency during daytime was decreased from 9.4 +/- 3.0 to 6.5 +/- 2.3 times after the 12-week treatment (P<0.001). The mean total OAB symptom score (OABSS) decreased from 7.7 +/- 4.2 to 3.1 +/- 3.1 after the 12-week treatment (P<0.001). The urgency and urgency urinary incontinence (UUI) domains significantly improved from the 12-week treatment, and complete resolution of urgency occurred in 38.9% of patients and the percentage of children with UUI among urgent patients decreased from 79.4% to 57.1%. According to 3-day voiding diaries, the average bladder capacity increased from 90.4 +/- 44.4 to 156.2 +/- 67.3 mL (P<0.001). Drug-induced adverse effects (AEs) were reported in 7 patients (20.6%). Our results indicate that solifenacin 5 mg fixed dose is effective against OAB symptoms, and its tolerability is acceptable without significant AEs in children with OAB.