There has been little study of the effect of clinical history on pathologic diagnostic accuracy. Five pathologists retrospectively examined 97 bronchial brush specimens with and without clinical historic information. Forty-nine patients had a biopsy-proven malignant lesion, and 48 had a benign lesion. Diagnostic accuracy with and without history for each pathologist was determined with likelihood ratios and receiver operating characteristic curves. The overall diagnostic accuracy with and without history was 0.84 and 0.76, respectively. The average negative predictive value of a benign diagnosis decreased from 89.2% (with history) to 74.0% (without history). Overall, the cytopathologists were more reluctant to make a definitive malignant diagnosis without history compared with history. The average positive predictive value of a malignant diagnosis with and without history was almost identical. The absence of history leads to lower diagnostic accuracy in the cytologic interpretation of bronchial brush specimens partly because pathologists underdiagnose malignant lesions.