Type 3c diabetes mellitus (T3cDM) is a secondary form of diabetes caused by pancreatic disease, such as chronic pancreatitis, that impairs insulin and glucagon secretion and results in poor glycemic control. Often misdiagnosed as type 2 diabetes, this pancreatic diabetes requires specific management due to elevated hemoglobin A1c levels, early insulin requirements, and increased risk of hypoglycemia. This case report discusses a 24-year-old man with hereditary chronic pancreatitis associated with the PRSS1 mutation, without typical symptoms of exocrine pancreatic insufficiency, who presented with early insulin therapy and increased glycemic variability. The complexity of diagnosing this type of diabetes highlights the importance of diabetes screening in patients with chronic pancreatitis and the risk of inappropriate diagnosis and medical treatment.