To compare the health-related quality of life (HRQoL) of overactive bladder (OAB) patients foilowing treatment with tolterodine extended-release (ER) 4 mg once daily versus placebo. Multinational, placebo-controlled, randomized, double-blind 12-week study. Patients with urinary frequency ( > or = 8 micturitions/24 hours over a 7-day period), urge incontinence ( > or = 5 episodes/week), and symptoms of OAB for at least 6 months were eligible for inclusion. Patients (81% female) received oral therapy with tolterodine ER (n = 507) or placebo (n = 508) for 12 weeks. HRQoL was assessed using the King's Health Questionnaire (KHQ) and Medical Outcomes Study Short Form 36-item questionnaire (SF-36). Patients also rated their bladder condition. Assessments were performed at baseline and at the end of treatment. At end of treatment, KHQ domains selected a priori as primary HRQoL end points (incontinence impact and role limitations) significantly improved (P < or = .001) with tolterodine ER. Domains selected a priori as secondary end points (physical limitations, sleep and energy, severity [coping] measures, and symptom severity) were also significantly improved (P < or = .006) following treatment with tolterodine ER. The tolterodine ER group had decreased symptom severity and statistically significant improvements in patient rating of bladder control compared with the placebo group at end of treatment. No treatment differences were detected using the SF-36. Many aspects of HRQoL, as measured by the KHQ, showed statistically significant improvement following treatment with tolterodine ER. These HRQoL improvements were consistent with clinical efficacy benefits. Patients receiving tolterodine ER experienced overall improvement in their condition that was associated with an important impact on their HRQoL.