To assess the onset of efficacy of fesoterodine 4 mg versus placebo in subjects with overactive bladder (OAB) symptoms Subjects who reported OAB symptoms for epsilon a parts per thousand yen3 months and recorded epsilon a parts per thousand yen8 micturitions and epsilon a parts per thousand yen1 urgency urinary incontinence (UUI) episode per 24 hours in 3-day baseline diaries were randomized to fesoterodine 4 mg, tolterodine extended release (ER) 4 mg, or placebo. This is an analysis of first week data from a 12-week, double-blind trial. ClinicalTrials.gov unique ID: NCT00444925 Baseline to week 1 changes in 3-day bladder diary variables, Patient Perception of Bladder Condition (PPBC), and Urgency Perception Scale (UPS) scores reported by subjects receiving fesoterodine 4 mg or placebo. By week 1, fesoterodine 4 mg (n == 679) was associated with significantly greater improvements compared with placebo (n == 334) in micturitions, urgency, severe urgency and UUI episodes, frequency-urgency sum, and MVV per 24 hours and 3-day diary-dry rate (all p < 0.05), but not nocturnal micturitions per 24 hours (p == 0.273). These differences were significant as early as day 5 of treatment (i.e., day 1 of the 3-day diary) for all diary endpoints except nocturnal micturitions and MVV. Changes in PPBC scores were significantly more favorable with fesoterodine 4 mg versus placebo (p == 0.0143); changes in UPS scores were not significantly different (p == 0.077). The results provide evidence that patients receiving fesoterodine 4 mg for their OAB symptoms may expect to experience a response as early as 1 week after initiating treatment. One limitation is that, although 65%% of subjects had received treatment with antimuscarinics before the study, whether subjects were dissatisfied with previous treatment and reasons for dissatisfaction were not collected. This might affect the magnitude of outcome improvements. Also, it is not known whether the UPS is sensitive enough to detect treatment differences as early as week 1.