In a pregnant woman who presents with acute pelvic pain and an adnexal mass, pregnancy-related etiologies, such as ectopic pregnancy or ovarian torsion, are typically the first diagnoses to be considered. Many other causes of pelvic pain associated with an adnexal mass can occur in pregnant patients, however. Some causes are benign and others require urgent management and treatment. Clinical presentation and physical examination can be misleading in pregnancy. The location of pain may be atypical for the pathologic entity, the pain may be muted, and in the case of infection, fever and leukocytosis can be absent. US examination is a safe and effective method for evaluating these patients. Sonographic characterization of adnexal masses may make a definitive diagnosis or focus the differential, which allows for prompt and appropriate treatment of patients.