A 26-year-old primigravida woman presented to the emergency department with mild cramping abdominal pain. She was approximately 7 weeks pregnant by the dates of her last menstrual period, and after a positive home pregnancy test had seen an obstetrician in a neighboring clinic 4 days prior to presentation. At the clinic the patient was told that her ultrasound revealed “a normal early pregnancy.” The patient was comfortable and well-appearing, in no acute distress, with normal vital signs. Her physical examination was unremarkable, and after a normal speculum examination the treating emergency physician performed a transvaginal ultrasound using an 8-5 MHz curvilinear endocavitary transducer (SonoSite MTurbo, Bothell, WA). There was no intrauterine pregnancy seen, but a large endometrial mass with multiple anechoic cystic structures resembling a “cluster of grapes” was identified (Figure 1). Dynamic imaging revealed that the mass was confined to the endometrium and did not demonstrate any free fluid in the cul-de-sac (Video Clip S1). The patient’s laboratory results were unremarkable with the exception of a human chorionic gonadotropin level of >260,000 mIU/mL. Given these results, a diagnosis of gestational trophoblastic disease (GTD) was made, and after urgent gynecologic consultation, the patient was admitted for dilatation and curettage. Coronal view of the uterus obtained with a high-frequency endocavitary transducer demonstrates endometrial mass (e) with anechoic cystic structures resembling a “cluster of grapes.” A thin layer of surrounding myometrium (m) is visible as well. Gestational trophoblastic disease is a term used to describe a number of placental pathologies including choriocarcinoma; placental trophoblastic tumor; and complete, partial, and invasive moles. Given the risk of malignancy (present in up to 20% of patients with complete hydatidiform mole and up to 3% of patients with partial hydatidiform mole), prompt diagnosis is of utmost importance. Because the symptoms of complete mole are nonspecific (vaginal bleeding, hyperemesis, hyperthyroidism) and the symptoms of a partial mole even more subtle, ultrasound remains the criteria standard for the diagnosis of GTD. The classic “snowstorm” pattern was described using older-generation ultrasound devices, and newer systems are more likely to demonstrate a complex intrauterine mass containing many small cystic structures. After diagnosis of GTD, a screening chest radiograph to evaluate for metastases should be obtained, and if there is any suspicion of invasive or metastatic disease, gynecologic oncology should be consulted. Video Clip S1. Dynamic imaging reveals that the mass was confined to the endometrium and did not demonstrate any free fluid in the cul-de-sac. The video clip is in QuickTime. Please note: Wiley Periodicals Inc. is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing material) should be directed to the corresponding author for the article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.