Pulmonary neuroendocrine tumors are currently considered to consist of three grades of malignancy, ranging from typical and atypical carcinoids to large-cell neuroendocrine carcinoma and small-cell carcinoma. The study reported here is the first population-based study of the demographics of patients with neuroendocrine tumors grouped by histological subtype. A cancer registry-based analysis of patients in Denmark in whom bronchial neuroendocrine tumor was diagnosed in 1978-97 was performed and the patients were followed up to 31 December 1999. Typical carcinoid was diagnosed in 105 patients, atypical carcinoid in 192, large-cell neuroendocrine carcinoma in 50 and small-cell carcinoma in 11,998. The recorded incidence of neuroendocrine tumors other than small-cell carcinoma increased by twofold among men (from 0.24 to 0.53 per 100,000 inhabitants per year) and by threefold in women (from 0.14 to 0.41 per 100,000 inhabitants per year) during the study period, while the incidence of small-cell carcinoma decreased among men and levelled off among women. The prognosis of patients with bronchial neuroendocrine tumors varied with the degree of malignancy; the 5-year survival rate ranged from 87% for patients with typical carcinoids, to 44, 15 and 2% for patients with atypical carcinoids, large-cell neuroendocrine carcinoma and small-cell carcinoma, respectively. In Denmark, the incidence of neuroendocrine tumours is increasing. Our findings support the pathological categorization of neuroendocrine tumors into three grades of malignancy. More research is needed to establish the etiological factors in the development of pulmonary neuroendocrine tumors.