Background: Neuroendocrine carcinomas (NECs) are diagnosed through a combination of immunohistochemistry (IHC) and morphology according to WHO guidelines. The presence of these crucial components for classification in the pathology report is critical for appropriate understanding of the report especially since terminology and definitions of NEC have been changing a lot lately. Objectives: The aim of this study is to assess the effect of WHO 2010 on the quality of pathology reporting for NEC and to assess the relevance of the criteria demanded. Methods: Patients registered with a NEC (gastrointestinal or unknown origin) in the Netherlands Cancer Registry (NCR) between 2008 and 2012 were included. Local pathology reports were reviewed for reporting of morphology and IHC comparing 2008-2010 (baseline) with 2011-2012. The diagnosis of NEC was confirmed according to WHO 2010, if synaptophysin or chromogranin were positive in a majority of cells and Ki-67 or mitotic count confirmed a grade 3 tumour. Results: 591 patients were registered with a NEC in the NCR. 436 pathology reports were reviewed. 62.2% of reports described morphology, IHC and grading in accordance with WHO 2010. Reporting of these parameters increased from 50.0% in 2008 to 69.2% in 2012. Large-cell NEC could be confirmed in 45.0% of patients, increasing from 31.7% in 2008 to 56.7% in 2012 (p = 0.02). Other diagnoses included neuroendocrine tumour (NET) G1/2 13.3%, small-cell carcinoma 2.8%, no neuroendocrine neoplasm (NEN) 17.7%, NEN grade unknown 21.3%. Mean survival was 1.1 years in large cell NEC versus 2.2 years in NET G1/2 (p = 0.005). Conclusion: Implementation of the WHO 2010 guideline is associated with a significant increase in reporting parameters needed for classification. Stratification of patients is more reliable based on reports containing all parameters. Guidelines alone however are not enough to warrant complete reporting; synoptic reports might be needed.