Fine-needle biopsy (FNB) is a valuable technique to use in the evaluation of thyroid nodules; however, false-negative and false-positive results do occur. At Sinai Hospital of Detroit (SHD) (Mich), a criterion was established for adequacy of an FNB specimen (ie, at least six clusters of benign cells on each of two slides prepared from separate aspirations) in an attempt to reduce the rate of false-negative diagnoses attributable to inadequate sampling. To evaluate the SHD criterion, 20 "problem" cases were selected from the SHD files and were reviewed by pathologists from three other institutions in a blind study. A total of 80 diagnoses were rendered (four institutions each reviewing 20 cases). Seven false-negative diagnoses were rendered, three of which were made in cases that did not meet the SHD criterion for adequacy. An additional three false-negative diagnoses on inadequate FNB specimens were made by a physician who asked not to be identified. Implementation of the SHD criterion may reduce the frequency of false-negative diagnoses. A separate study was undertaken to determine the number of FNB aspirations necessary to obtain satisfactory specimens. One hundred adequate FNB specimens from SHD files were reviewed. In 77% of cases the first two to four aspirations were adequate, but 23% of the time six to eight aspirations were necessary to obtain adequate material.