​Many tumours are non-functional, and are therefore asymptomatic. They may be discovered on imaging performed for other unrelated reasons.

Functional tumours may produce symptoms related to the hormones secreted. They may cause gastric or intestinal ulcers, result in low or high blood sugar levels, or produce flushing and diarrhoea. However, most patients who have these symptoms do NOT have a pancreatic endocrine tumour.

In addition, advanced tumours that are large may produce symptoms such as blockage of the bile duct (jaundice) or intestine (obstruction). These tumours are more likely to be malignant, and should be removed.