Fine needle aspiration cytology (FNAC) has been known as a very sensitive and effective method for preoperative diagnosis. We studied cases preoperatively diagnosed by FNAC and confirmed by the histopathologic examination to define the effectiveness of FNAC. A total of 567 cases including breast, thyroid gland, lymph node, and soft tissue confirmed histologically after FNAC were enrolled, among 2,844 FNAC cases from January 1996 to March 2000. Overall sensitivity and specificity of FNAC were 93% and 100%, respectively. Sensitivity and specificity of FNAC by sites or organs were 91% and 100% in breast, 100% and 100% in thyroid, 97% and 100% in lymph node, and 71% and 100% in soft tissue, respectively. Nine cases showed diagnostic discrepancy; eight cases of sampling error and one case of interpretation error. Five cases, diagnosed as fibrocystic change at FNAC but invasive ductal carcinoma after the histopathologic examination, were categorized as sampling error due to the presence of diffuse fibrosis or deep seated location. One case of breast, diagnosed descriptively as atypical ductal and stromal cells suggesting invasive ductal carcinoma at FNAC but malignant phyllodes tumor histologically, was categorized as interpretation error. Other cases of sampling errors were two cases of soft tissue, a case of lymph node, and a case of salivary gland.