Tracheobronchial neuroendocrine tumours can be divided into 4 main groups: typical carcinoid; well-differentiated neuroendocrine carcinoma (atypical carcinoid); neuroendocrine carcinoma of the intermediate type, and small-cell carcinoma. Typical and atypical carcinoids are differentiated tumours, whereas intermediate neuroendocrine tumours and small cell carcinomas are little or not differentiated. Morphological or architectural criteria usually suffice to distinguish between carcinoid tumours and small cell carcinomas. In some cases, however, the neuroendocrine nature of poorly differentiated and non-small cell carcinomas is suggested by morphological criteria, but it can be confirmed only by immunohistochemistry and electron microscopy. Tracheobronchial neuroendocrine tumours of the intermediate type have been studied from a first, well-documented clinical case which demonstrated two important points: the prognosis of these tumours seems to be worse than that of carcinoid tumours, and they favourably respond to chemotherapy. In view of the therapeutic consequences, it is necessary to investigate, by the appropriate techniques, the neuroendocrine nature of these poorly differentiated carcinomas.