In 1990, the College of American Pathologists Q-Probes Quality Assurance Program studied performance in fine-needle aspiration (FNA) of pulmonary lesions derived by retrospective analyses of cases accessioned throughout 1989 by 436 institutions in North America. The aggregate database consisted of 13,094 lung FNA cases with 11,922 (91%) judged as satisfactory for cytologic evaluation. Of these satisfactory aspirates, 5264 (40%) had corresponding histologic tissue biopsy preparations and FNA diagnoses available for further evaluation and formed the basis for determining diagnostic accuracy. There was no significant difference in overall performance results derived from the data provided by all participants compared with the median of those reporting a greater number of correlated FNA cases. In the diagnosis of lung cancer by FNA, the following performance results were derived using the aggregate database: 89% sensitivity of FNA procedure, 99% sensitivity of FNA diagnosis, 96% specificity, 99% positive predictive value, 70% negative predictive value, 91% efficiency, 0.8% false-positive FNA interpretation, and 8% false-negative rate. The aggregate value and median performance values of sensitivity and specificity derived from this Q-Probe study, which reflects the general practices of mostly non-university hospitals in North America, compare very favorably with study results of similar design in the literature reflecting practices from academic centers. This appears to validate published rates from academic centers as reproducible in the general practice of pathology and validates the use of these values derived from an aggregate database as a benchmark to measure performance improvement in lung FNA.