This study aimed to determine the reasons for sampling and interpretative errors in false ‎negative and false positive diagnoses of breast carcinoma on fine-needle aspiration ‎cytology (FNAC) material. The study design is that a totally 912 cases of breast FNAC were ‎performed between 2000 and 2004, and 126 cases of them were diagnosed as breast ‎carcinoma. Only those cases with cytohistological discrepancies were cytologically reviewed, ‎in which the cytological material was abnormal and to some extent misinterpreted or both. ‎There were 8 false negative diagnoses (false negative rate 6.3%) and 3 false positive ‎diagnoses (false positive rate 2.3%). The results of this study showed that among 8 false ‎negative cases, 5 showed hypocellular smears with minimal nuclear pleomorphism of the ‎cells. Histology revealed 3 infiltrating ductal carcinomas of scirrhous subtype and 2 ‎infiltrating lobular carcinomas. The smears of other 2 false negative cases, which ‎histologically verified as well-differentiated infiltrating ductal and pure intraductal carcinomas, ‎were hypercellular and composed predominantly of groups of cohesive, small, and uniform ‎cells simulating fibroadenoma or fibrocystic changes. Smear of the last false negative case ‎‎(histologically verified as infiltrating ductal carcinoma with extensive cystic degeneration) ‎revealed large sheets of macrophages and degenerated epithelial cells on inflammatory ‎background. In 3 false positive cases, 2 were histologically proved as fibroadenoma and 1 ‎fibrocystic changes. Smears of the 2 false positive fibroadenomas showed very high ‎cellularity, overlapped clusters, and frequent stripped bipolar nuclei. The fibrocystic case ‎showed tight clusters of apocrine cells and sheets of loosely aggregated macrophages that ‎were over interpreted. The conclusion of this study is that hypocellularity and relatively ‎nuclear monomorphism are the reasons for failure to diagnose breast carcinoma. Careful ‎attention should be paid to extreme nuclear monomorphism and absence of naked bipolar ‎nuclei. So awareness of smear cellularity and subtle cytological features will aid in the correct ‎preoperative diagnosis of lobular; scirrhous; and intraductal carcinomas, and false negative ‎diagnoses can be minimized. A cytologically atypical or suspicious diagnosis together with ‎positive mammographical and clinical findings should suggest a diagnosis of malignancy. ‎Hypercellular smears with overlapped clusters should be carefully assessed for uniformity of ‎the cells and detailed nuclear features. If the full-blown malignant cytomorphological features ‎are not visible, a diagnosis of suspicious or inconclusive should be made and frozen section ‎Created by Wameed Al-Hashimy intraoperative imprint cytology is recommended before ‎surgery.‎