Background : Second opinion diagnosis of outside pathology slides is a common practice for efficient and proper patient management. We analyzed cytology slides from outside hospitals submitted for a second opinion diagnosis to determine whether the second opinion diagnosis had any influence on patient care. Methods : We reviewed 1,153 outside cytology slides referred to Asan Medical Center for second opinions from January, 2007, to December, 2007. All cases were categorized into three groups; no diagnostic discrepancy, minor diagnostic discrepancies (no impact on the management), and major diagnostic discrepancies (significant impact on the management and subsequent follow-up). Results : The thyroid was the most common organ system (933 cases, 80.9%), Forty cases (3.6%) belonged to the major diagnostic discrepancy group and 149 cases (12.8%) to the minor discrepancy group. For validation of second opinion diagnoses in major discrepancy cases, subsequent biopsy or surgical resection specimens and clinical information were reviewed, which were available in 29 cases. The second opinion diagnoses resulted in alteration of clinical management in 21 of 29 cases. Conclusion : For all referred patients, second opinion diagnosis is important and mandatory for appropriate patient care.