Pulmonary neuroendocrine, or Kulchitsky-type, cells are sparse airway epithelial cells that release bioactive amines and the peptides serotonin, chromogranin A, gastrin-releasing peptide (GRP), and calcitonin. Neuroendocrine hyperplasia is a premalignant finding limited to the basement membrane or airway wall and occurs spontaneously or as a reactive process. Neuroendocrine cellular proliferations measuring < 5 mm are classified as carcinoid tumorlets. Carcinoid tumors are > 5 mm. Coexistence of all three often occurs in DIPNECH. DIPNECH is found in 5% of patients undergoing carcinoid resection. The gold standard for diagnosis is surgical biopsy, although the more recent literature suggests transbronchial biopsy may be adequate if sufficient tissue is obtained. The typical finding is diffuse hyperplasia of neuroendocrine cells with multiple carcinoid tumorlets and peribronchial fibrosis that focally obliterates airways (Figs 1, 3, 4). Interstitial fibrosis associated with DIPNECH is postulated to be secondary to the production of bombesin and GRP, which stimulate fibroblasts and, with elevated serotonin levels, enhance bronchoconstriction. The result is dyspnea, cough, and wheeze that should be distinguished from other etiologies of bronchoconstriction such as bronchial asthma, as bronchodilator therapy in patients with DIPNECH may have little benefit. These airway changes can be seen as obstructive disease on pulmonary function testing and can produce the mosaic pattern seen on high-resolution CT scanning. Neuroendocrine cell hyperplasia can be seen on hematoxylin and eosin staining, but is readily apparent via synaptophysin and chromogranin immunostaining (Fig 1). It consists of groups of polygonal cells with round uniform nuclei in the basal region of the bronchiolar epithelium. In this case, immunohistochemical stains of the carcinoid tumor demonstrated expression of chromogranin A and synaptophysin, but no expression of p63 and CK5/6 (Fig 5). These tumors can also show expression of GRP, calcitonin, and human chorionic gonadotropin (hCG)-α. Neuroendocrine tumors associated with DIPNECH are usually typical carcinoids, although there are several reported cases of atypical carcinoid associated with DIPNECH. In 2015 the WHO defined DIPNECH as a proliferation of pulmonary neuroendocrine cells that can be limited to bronchial mucosa, extend locally to form tumorlets, or develop into carcinoid tumors. The patient presented met these criteria. Pulmonary neuroendocrine cell hyperplasia not meeting these criteria can occur in a number of other conditions such as tobacco smoke inhalation, chronic high-altitude exposure, bronchiectasis, and interstitial fibrosis. The diagnosis of DIPNECH is considered to be a precursor to malignancy and the literature does describe patients receiving a diagnosis of DIPNECH before the diagnosis of a carcinoid tumor. However, the majority of patients receive simultaneous diagnoses of DIPNECH and carcinoid tumor.