Chronic diarrhea is a common complication of cancer or chemotherapy. It is rare as the only symptom of neoplastic disease, and depending on its etiology and mechanism of its formation, may be osmotic, secretory, fatty, inflammatory and associated with accelerated intestinal transit. In the discussed case, the most common disease states leading to the destruction of the mucosa of the small intestine were excluded. The cause of diarrhea in the patient was determined only after an autopsy. The secretive neoplastic disease should be taken into account in the differentiation of chronic diarrhea.