Idiopathic detrusor instability was diagnosed as the cause of urinary incontinence in 2 dogs and a cat. The diagnosis was based on abnormal cystometrographic findings and by exclusion of other causes of detrusor hyperactivity. Anticholinergic or combined anticholinergic, antispasmodic, and local anesthetic treatment resolved the clinical signs in all 3 animals. Increased threshold volumes after treatment were documented by cystometrography in one dog and in the cat.