Spontaneous rupture of gastrointestinal stromal tumor (GIST) with hemoperitoneum is an extremely rare clinical presentation of this mesenchymal tumor. We report the unusual case of a 68-year-old man who was admitted to the hospital with abdominal pain. While waiting for the results of his laboratory tests the patient became pale and tachycardic and his abdomen distended with generalized rebound tenderness. A CT scan suggested rupture of a cavernous angioma of the liver and the patient was brought to the operating room for an explorative laparoscopy, which revealed hemoperitoneum from a ruptured giant gastric GIST. After conversion to laparotomy, the tumor was excised: it was 11 x 10 x 5 cm in size, with massive necrosis and clotted blood inside. Immunohistochemical examination revealed reactivity to c-KIT and CD34, consistent with the diagnostic criteria for GIST, with low mitotic activity (< 5/50 HPF). The postoperative course was uneventful, and the clinical and radiological follow-up at 6 months is negative for recurrence.