Amyloidosis with gastrointestinal involvement is a rare cause of chronic diarrhoea, and should be considered especially in adult patients with intestinal malabsorption and extra GI manifestations. We present the case of a male patient who, after an oncological gastrectomy, presented with chronic diarrhea that did not respond to treatment and, after study, the cause of the diarrhea was finally found. Primary systemic light chain amyloidosis (AL) initially presents as chronic diarrhea and weight loss after gastrectomy.