BACKGROUND: The histologic criteria to classify follicular thyroid neoplasms are controversial. Criteria used for diagnosis and treatment varies both within and between specialty groups. This discordance makes it difficult to compare disease and management practice. This is especially problematic in issues concerning reoperations and survival. To determine the degree of disparity, we surveyed 3 groups of specialists. METHODS: A questionnaire describing 10 histologic scenarios was sent to an equal number of thyroidologists, endocrine surgeons, and endocrine pathologists. Individuals were randomly selected from rosters of 3 corresponding societies. Each item asked for a rating of a diagnosis and treatment. Questionnaires were distributed and received by facsimile, and responses were kept confidential. The response rate was 60%. RESULTS: Responses were analyzed by nonparametric statistical tests. Two scenarios had significant disagreement among specialties in both diagnosis and treatment: one scenario involved the assessment of neoplasms with minimal capsular invasion; the other scenario involved Hürthle cell features. In both scenarios pathologists tended to be more conservative in assigning the term carcinoma and recommending total thyroidectomy. Significant disagreement within specialty groups was also noted. Two other scenarios dealt with the distinction between minimally and widely invasive carcinoma; significantly, pathologists viewed tumors as less invasive. CONCLUSIONS: This study indicates that much disparity exists among specialists in pathology, endocrinology, and surgery and among experts in each of these disciplines. It highlights that there is no uniform classification. If multicenter trials to evaluate treatment options are to occur, a universal classification must be accepted.