Tolterodine is approved for use in the treatment of overactive bladder (OAB). The study is designed to a investigate whether pregabalin may have efficacy in OAB and whether the efficacy is altered when it is combined with tolterodine.

Inclusion Criteria:

• Women > 18 years Old
• Diagnosis of OAB (micturition frequency >/= 8 times per day; urinary urgency >/= 4 times per week)

Exclusion Criteria:

• Subjects with symptoms of overactive bladder for less than 6 months prior to randomization.
• Significant stress incontinence as determined by the investigator e.g. stress predominant mixed incontinence, positive cough provocation test.
• Subjects with any condition that would contraindicate the use of tolterodine or pregabalin, including: Uncontrolled narrow angle glaucoma; Urinary retention; Myasthenia gravis; Gastric retention; Severe ulcerative colitis; Toxic megacolon; Rare hereditary problems of galactose intolerance; Fructose intolerance; Sucrose-isomalate insufficiency; Lapp lactase deficiency; Glucose-galactose malabsorption.