The aim of this study was to review the diagnostic significance of pancreatic polypeptide (PP) in pancreatic diseases. PP may play a significant role in monitoring the development of the disease and the patient's healing process, particularly after the removal of a portion of the pancreas. Determining PP in acute pancreatitis is quite controversial. At the 1st stage of severe pancreatic damage, there is excessive PP release followed by its fall. In patients with chronic pancreatitis, a significant decrease in PP secretion was found in the presence of a food stimulant. In this case, PP could be a good marker for determining the stage of pancreatitis. Pancreatic polypeptide also functions as a hepatic glucose regulator. PP increases hepatic insulin sensitivity, resulting in reduced hepatic glucose production. Therefore, impaired hepatic insulin sensitivity in chronic pancreatitis is abrogated after the PP administration. Endocrine pancreatic tumors initially grow without specific symptoms. In contrast, they are almost always correlated with elevated serum pancreatic polypeptide. Therefore, the level of PP may be a good diagnostic parameter confirming the presence of pancreatic cancer. Depending on the type of disease, the polypeptide concentration can be increased or decreased, evidencing the disease progress or regression.