Detrusor instability is a common cause of urgency and urge incontinence in neurologically normal patients. It is defined as an involuntary phasic detrusor contraction of any pressure associated with symptoms of urge or leakage while the patient is attempting to inhibit micturition. The etiology is unknown but it has been associated with congenital causes, aging, stress incontinence, and bladder outlet obstruction. Diagnosis relies on a urologic history and physical examination, a voiding diary, and a urodynamic evaluation. Treatment is primarily pharmacologic and behavioral, with surgical options being reserved for selected patients.