Context.-Study comparisons rest on the assessment of applicability or external validity. Population characteristics are an important component of external validity and, although there has been a heightened awareness of deficiencies in reporting in diagnostic test accuracy (DTA) studies, the reporting of populations in DTA studies has not been investigated. Objective.-To assess the quality of reporting of population descriptions in DTA studies for fine-needle aspiration cytology (FNAC). Design.-Literature survey of common population parameters and usage patterns in FNAC DTA studies. We randomly selected 20 FNAC DTA studies in 4 categories (salivary glands, lung, thyroid, and pancreas) and determined the frequency of parameter usage. Results.-Studies showed considerable variability in reporting patterns. On average, studies reported 2 to 4 parameters to describe study populations. Age, sex, and lesion size were most frequently reported. Sixteen percent of studies did not provide any population description. Population parameters were used to describe the sample population more frequently than to describe the selection process (P = .001). There were significant differences in the number of parameters specified by anatomic site (P = .001). Only 21% of studies provided a flow diagram. Thirty-three percent of studies mentioned the target population. Conclusions.-Studies show considerable variability in the description of sample populations and the population selection process. Studies often fail to provide flow diagrams or to provide a clear statement of the research problem. There is considerable opportunity for studies to improve both descriptions of sample populations and the process used to select them.