Irregular vaginal bleeding is a common symptom of women seeking gynecologic care. Etiologies of irregular vaginal bleeding can be classified into the following categories: pregnancy related (retained products of conception, threatened or missed abortion, or ectopic pregnancy), hormonal (disorders of ovulation, menopause, or hormonal contraceptive use), structural (polyps, myomas, or arteriovenous malformation), neoplasm (endometrial cancer), and infection (endometritis). After the history and physical examination, the initial evaluation of irregular vaginal bleeding has traditionally involved an endometrial biopsy. Transvaginal ultrasound has revolutionized the evaluation of the gynecologic ultrasound examination by providing a minimally invasive means to determine the etiology for the bleeding. Transvaginal ultrasound assessment of the endometrial cavity allows treatment to be tailored to the specific cause of irregular vaginal bleeding, thus saving women time, money, and exposure to unnecessary interventions. The purpose of this article is to give the clinician critical information regarding the capabilities of ultrasound to evaluate women with irregular vaginal bleeding.