Primary leiomyosarcoma of greater omentum is rare and mimics gastrointestinal stromal tumor (GIST) due to their common origin. A 65 years old male presented with a large mass per abdomen of one year duration. Imaging findings were suggestive of extra-gastrointestinal stromal tumor (E-GIST) arising from greater omentum. The mass was excised. On microscopy, the diagnosis of leiomyosarcoma and E-GIST were considered. The tumor cells showed immunoreactivity for smooth muscle actin, muscle-specific actin, heavy-caldesmon and desmin and were immunonegative for CD117, DOG1 and CD34, hence confirming primary leiomyosarcoma of greater omentum. We present this case for its rarity.