The acceptance of fine-needle aspiration biopsy in the diagnostic work-up of pulmonary masses has resulted in an increased number of neuroendocrine tumors of the lung first encountered as aspiration cytology specimens. The accurate cytologic identification of these neuroendocrine neoplasms is important in that they have relatively specific clinical and prognostic features in contrast to nonneuroendocrine neoplasms. We report on the cytologic features of 46 primary pulmonary neuroendocrine neoplasms initially encountered on fine-needle aspiration biopsies. The neoplasms are separated into three distinct cytologic groups, including the typical carcinoid (13 cases), the atypical carcinoid (3 cases), and small-cell carcinomas (30 cases). The clinical features of all cases--and histologic findings when they were available--are also considered. Finally, a detailed cytologic description of the three groups of neuroendocrine neoplasms is presented with emphasis on differential diagnosis including nonneuroendocrine pulmonary neoplasms.