Objectives: Breast disease remains a major public health issue worldwide. It is the most common cancer among Nigerian women. Fine needle aspiration cytology (FNAC) is an important preoperative assessment tool along with clinical and mammography examination in both screen detected and symptomatic breast disease. This study provide opportunity to determining the accuracy of FNAC and factors affecting false negative rate in Obafemi Awolowo University Teaching Hospital complex, Ile-Ife, Osun state Nigeria Method: All patients seen in the breast clinic with lump were sent to the pathology department for FNAC from January 1997 to December 2004.The sociodemographic data; cytology result, final histology result and the clinical staging for breast cancer were analyzed. Results: Eight hundred and sixty-four patients had FNAC during the studied period, however only 632 cases had available final histological report. Of these, 20 (3.2%) were male while 612 (96.8%) were female, the age ranged from 15 years to 99 years, median of 36.50. We found that absolute sensitivity for malignancy to be 70.8%. The false negative rate was 14.9%, while the false positive rate was 1.8%. The suspicious rate was 9.8% while the inadequate rate was 5.4%. Conclusion: FNAC remains the least invasive, the most rapid and the most cost effective method to confirm clinical and radiological suspicion of malignancy, however, the test has high false negative rate. We recommend that consultation between pathologists and the clinicians should be facilitated and encouraged to reduce the high false negative. Also, multi-disciplinary audits of difficult case should be part of the work routine.