Acute pelvic pain is defined as noncyclic, intense pain localized to the lower abdomen and/or pelvis, with a duration of less than three months. Signs and symptoms are often nonspecific. The differential diagnosis is broad, based on the patient's age and pregnancy status and gynecologic vs. nongynecologic etiology. Nongynecologic etiologies include gastrointestinal, urinary, and musculoskeletal conditions. Urgent gynecologic conditions include ectopic pregnancy, ruptured ovarian cyst, adnexal torsion, and pelvic inflammatory disease. Approximately 40% of ectopic pregnancies are misdiagnosed at the presenting visit. Urgent nongynecologic conditions include appendicitis and pyelonephritis. Less urgent etiologies include sexually transmitted infections, pelvic floor myofascial pain, dysmenorrhea, and muscle strain. Approximately 15% of untreated chlamydia infections lead to pelvic inflammatory disease. History and physical examination findings guide laboratory testing. Questions should focus on the type, onset, location, and radiation of pain; timing and duration of symptoms; aggravating and relieving factors; and associated symptoms. Performing a urine pregnancy test or beta human chorionic gonadotropin test is an important first step for sexually active, premenopausal patients. Imaging options should be considered, with transvaginal ultrasonography first, followed by computed tomography. Magnetic resonance imaging can be useful if ultrasonography and computed tomography are nondiagnostic.