BACKGROUND: We reported a case of malignant nonfunction islet cell tumor (10.0 cm in diameter) of the pancreas, with malignant histological features and splenic inifltration. The case is rare, and few reports have been published. METHODS: A 46-year-old woman with a vague pain in the left upper quadrant for 3 months was found to have a tumor in the spleen. Ultrasonography and computed tomography demonstrated a well-deifned pancreatic tumor of 8.2×10.0 cm in size, her serum levels of pancreatic hormones were within normal limits. RESULTS: Splenectomy combined with pancreatectomy was performed for the tail of the pancreas. Resected specimens showed a malignant nonfunctioning islet cell tumor invading the spleen. CONCLUSIONS:The growth pattern of the tumor causes malignant features. Resection of the tumor should be performed by enucleation, pancreaticoduodenectomy or distal pancreatectomy.