Gastrointestinal stromal tumors (GISTs) are rare mesenchymal neoplasms of the digestive tract. Synchronous occurrence of a gastrointestinal stromal tumor with a tumor of different histogenesis is very rare and has been documented in the literature mainly in case reports. We present the case of a 78-year old female patient who underwent surgery for an advanced gastric carcinoma during which a gastric stromal tumor was incidentally discovered. A review of the literature is also conducted on the extremely rare synchronous occurrence of malignant tumors of different histogenesis in the stomach.