Neuroendocrine tumors (NETs) are rare. However, several data showed the incidence is increased in the past 30 years. NETs can be both functional and non‐functional, and may be undetected for years without obvious signs or symptoms. NET are classified as G1 (carcinoid), G2, G3 (large cell or small cell type), mixed adenoneuroendocrine carcinoma (MANEC), hyperplastic and preneoplastic lesions according to WHO classification 2010. NETs are often advanced at the time of diagnosis and is a progressive disease. Outcomes in patients with locally inoperable or metastatic NETs are poor, survival is also associated with tumor grade. Diagnosing NETs is the systematic approach. History taking and physical examiantion are essential and biochemical markers are useful. Imaging studies, somatostatin‐receptor scintigraphy (Octreoscan™), CT scan, MRI and/or PET scan can be used. Somatostatin receptor analogues showed symptomatic, biochemical and disease control. Targeted agents such as everolimus and sunitinib also showed benefit for advanced pancreatic NETs. Other treatments including peptide receptor radionuclide therapy (PRRT), hepatic regional therapy for liver metastases (arterial embolization, chemoembolization), or ablative therapy can be used. Chemotherapy, such as streptozotocin, 5‐fluorouracil, doxorubicin, dacarbazin, etoposide, cisplatin, temozolomide, capecitabine is another option for the treatment of NETs. In conclusion, NETs are no longer rare disease. If we raise the index of suspicion for NETs, we can detect these tumors as earlier as possible. Local treatment is unique option for cure in earlier stage. The treatment for patients with advanced NETs, symptom and disease control is important with multidisciplinary team approaches. (Korean J Med 2013;85:354-356)