Inclusion Criteria:

• Patients with OAB who have been treated with tolterodine tartrate extended release for at least 4 weeks immediately preceding entry into the study, and wish to switch to solifenacin succinate due to lack of sufficient improvement in urgency episodes.
• Previous non-drug treatment of OAB is allowed if it has been established at least 4 weeks prior to Screening and is continued throughout the study.
• At least 3 urinary urgency episodes/24 hours while receiving tolterodine tartrate extended release documented in a 3-day patient diary in the pre-washout assessments on tolterodine tartrate extended release with or without urge incontinence described as OAB syndrome.
• Prior to treatment with tolterodine tartrate extended release, patients must have had OAB syndrome for 3 or more months.

Exclusion Criteria:

• Previous treatment with darifenacin
• Treatment with tolterodine tartrate extended release for less than 4 weeks prior to enrollment in the study.
• Significant stress incontinence or mixed stress/urge incontinence where stress is the predominant factor as determined by the investigator.
• Evidence of a urinary tract infection; chronic inflammation such as interstitial cystitis and bladder stones.
• Clinically significant outflow obstruction as determined by the Investigator
• Uncontrolled narrow angle glaucoma, urinary or gastric retention.
• All patients with severe renal or hepatic impairment will be excluded
• Patients with chronic severe constipation or history of diagnosed gastrointestinal obstructive disease.