In 1975 at Duke University Medical Center, a retrospective and prospective survey of respiratory cytopathologic specimens was undertaken for the ten-year period 1970 to 1979. The purpose of this study was to document the role of cytopathology in the diagnosis of lung cancer at this institution. This paper, the first of a series on the subject, presents the relationship between the number of cytopathologic specimens examined, the types of respiratory cytopathologic specimens examined and the cytopathologic diagnosis of lung cancer during the first five years of the study. Of the total, 363 patients had respiratory cytopathologic specimens that were interpreted as being diagnostic of cancer. Among those patients with cytopathology diagnostic of cancer, a diagnosis was made with five satisfactory specimens in 86.6%. Sputum only revealed neoplastic cells in 47.1% of the cases, bronchial material only in 26.0% and both sputum and bronchial material in 26.9%. Among the total number of primary lung cancers seen during this five-year period, a definitive cytopathologic diagnosis of cancer was made in approximately 50% of cases.