BACKGROUNDTouch preparations (TPs) can be performed for on‐site adequacy assessment of core needle biopsies (CNBs). Although TPs can play a role in decreasing the number of nondiagnostic core biopsies, the impact of TPs on CNB has not been extensively evaluated.METHODSComputerized tomography–guided CNBs performed in a tertiary cancer center were retrospectively identified. On‐site adequacy assessment was performed in all cases. The matching TPs and CNBs were evaluated for diagnostic accuracy of the TP. The relation between the site of biopsy and the cellularity of the CNB was also analyzed.RESULTSA total of 1100 CNB cases with associated TPs were identified over a 6‐month period. Eighty‐four cases (8%) showed marked differences in cellularity between CNB and TP, and 43 of these 84 cases (4.3%) showed the presence of diagnostic cells in either CNB or TP, but not in both. Lung was the biopsy site where CNB was most affected by loss of diagnostic cells.CONCLUSIONSTP and CNB findings must be integrated to prevent a misdiagnosis. Lung CNBs were more frequently affected by performing TPs. Cancer (Cancer Cytopathol) 2014;122:851–854. © 2014 American Cancer Society.