In addition to a description of the basic criteria for the diagnosis of papillary carcinoma, a review of discussions by all workshop participants on the illustrative cases is presented. Areas of consensus included the following: classification of mixed papillary and follicular carcinomas as papillary, regardless of follicular dominance; recognition of three morphological variants--follicular, encapsulated, and diffuse sclerosing; nonspecificity of individual histological criteria, with the necessity to utilize a combination of characteristic features as guidelines for establishing a diagnosis; citing of nuclear features as probably the most important diagnostic criteria, ie, increased N/C ratio, irregularity in outline, and paleness of staining (ground glass appearance); grading of tumors on the basis of either cytological or architectural characteristics remains of unproven prognostic value. (Gross extent of tumor at the first operation remains the most valuable single prognostic criterion.); defining small carcinomas by size rather than using the imprecise term "occult" with its variable definitions including some clinically evident tumors; classifying as undifferentiated those carcinomas presenting a mixed papillary and anaplastic appearance at the time of the first operation, and retaining the papillary designation for papillary cancers which later undergo dedifferentiation; and recognition that thyroglobulin is a constant and keratin an inconstant tumor cell marker, with the latter not specific for distinguishing papillary carcinomas from follicular carcinomas or from hyperplastic adenomas.