SUMMARY: Solid pseudopapillary neoplasm (SPN) is classified as an epithelial tumor identified from benign to low-grade malignant tumor. It is a relatively rare tumor among various pancreatic tumors and is generally observed in young women. Therefore, the identification of an SPN should be considered in cases where a solid/cystic mass is detected in the pancreas of a young woman. Distal pancreatectomy is performed for a large size of SPN located in the tail of the pancreas. Here, we report a 15-year-old Japanese female who brought about Type 3C diabetes mellitus (T3C-DM) after a distal pancreatectomy due to SPN. This case highlights the importance of management after pancreatectomy to detect early T3C-DM and prevent its development even in young patients. Although it is not surprising that a massive pancreatic tumor or pancreatectomy can lead to pancreatic diabetes at any age, we believe that it is important for clinicians to know this subject for educational purposes. LEARNING POINTS: SPN is a relatively rare tumor that accounts for 1-3% of all pancreatic tumors and is predominantly located in the tail of the pancreas.Since SPN is generally observed in young women, the presence of an SPN should be considered in cases where a solid/cystic mass is detected in the pancreas of a young woman.Pancreatic DM after pancreatectomy is classified as T3C-DM in the American Diabetes Association (ADA) classification.This case indicates that even in young individuals, it is important to consider the possibility of impaired glucose tolerance after distal pancreatectomy.