['In multidisciplinary assessment clinics for screen-detected breast lesions, onsite cytopathologists provide immediate results of fine-needle aspiration biopsies (FNABs) and this information is used for patient counseling and treatment planning. Such consultation is not possible for the increasing proportion of lesions that are being assessed by core biopsy. If core imprint cytology (CIC) of breast cores can be shown to be reliable in a significant proportion of screen-detected lesions, this technique may be of clinical value in such clinics.', 'In the setting of a large, accredited, population-based breast cancer screening program, prospective results of CIC were gathered on 567 lesions and correlated with the results of core biopsy to determine the performance indicators for CIC.', 'The positive predictive value of a diagnosis of malignancy on CIC was 98.2% and the negative predictive value was 77.8%. The absolute sensitivity was 42.2%, complete sensitivity (inclusive of suspicious and atypical results) was 86.4%, absolute specificity was 56.3%, and total specificity (inclusive of acellular imprints) was 83.7%. The 2 false-positive imprints had atypical ductal hyperplasia on core histology but were found to be ductal carcinoma in situ (DCIS) on excision. False-negative imprints are a greater challenge, with 13.6% of malignant lesions producing benign-appearing or acellular imprints. Low-grade DCIS, lobular, and special type cancers account for most such lesions. The results of the current study also demonstrated significant variations in the accuracy of CIC in microcalcifications versus parenchymal lesions. In particular, the results of acellular imprints are analogous to benign CIC findings for microcalcifications but not in parenchymal lesions.'] Is core imprint cytology of screen-detected breast lesions predictive of the histologic results?