While most people with diabetes have type 2 disease, a non-negligible minority develops a secondary diabetes. Post-pancreatitis diabetes mellitus (PPDM) is an exemplar secondary diabetes that represents a sequela of pancreatitis - the most common disease of the exocrine pancreas. Although this type of diabetes has been known as a clinical entity since the late 19th century, early 21st century high-quality epidemiological, clinical, and translational studies from around the world have amassed a sizeable body of knowledge that have led to a renewed understanding of PPDM. People have at least two-fold higher lifetime risk of developing diabetes after an attack of pancreatitis than those in the general population without history of diseases of the exocrine pancreas. PPDM is caused by acute pancreatitis (including non-necrotising pancreatitis, which constitutes the majority of acute pancreatitis) in four-fifth of cases and chronic pancreatitis in one-fifth of cases. Moreover, the frequency of incident diabetes is not considerably lower after acute pancreatitis than after chronic pancreatitis. Recurrent attacks of pancreatitis and exocrine pancreatic dysfunction portend high risk for PPDM, but are not mandatory for its development. Further, young- or middle-aged non-obese men have an increased risk of developing PPDM. In comparison with type 2 diabetes, PPDM is characterised by poorer glycaemic control, higher risk of developing cancer (in particular, pancreatic cancer), younger age at death, and higher risk of mortality. Metformin monotherapy is recommended as first-line therapy for PPDM. Appropriate screening of individuals after an attack of pancreatitis, correct identification of PPDM, and apposite management is crucial with a view to improving the outcomes of this secondary but not inappreciable disease.