To determine if previous experience with the cytologic presentation of pleomorphic adenoma (PA) results in a lower number of diagnostic errors. Comparative analysis of the diagnostic accuracy of PA during 2 periods (1980-1994 and 1995-2003). The first period included 198 tumors and the second, 230. Diagnostic errors were divided into major or minor according to the consequences for patient management. Major errors were considered those that could result in an erroneous surgical approach or treatment delay. Concordant results increased from 88.4% to 91.2%. Sensitivity rose from 92.6% to 95.5%. The false negative rate diminished from 7.1% to 4.5%. Regarding malignancy, false negative diagnoses diminished from 5 to 3. The second period included no false positive diagnoses of malignancy, while the first had 3. A total of 42 errors were present, 6 of them were nonrepresentative cases. Thirteen of the remaining 36 (36.1%) were considered major errors, while 23 (63.9%) were classified as minor errors. Major errors diminished from 8 to 5. The most significant reduction in errors occurred in the category of PA showing cystic transformation. Cytologic diagnostic accuracy of PA is high, and major errors may diminish if special attention is paid to some pitfalls. Sampling limitations and interpretive difficulties may prevent differentiation from afew cases of carcinoma ex-PA and adenoid cystic carcinoma (ACC). A few diagnostic errors are difficult to avoid. Small tissue biopsies will not resolve these problems.