Among the patients directed to the Department of Endocrinology of the Institute of Internal Medicine for diagnostic examinations of the thyroid, 726 (647 women and 79 men, of age between 16 and 79 years) were qualified to surgery after scintigraphic detection of cold nodules. From this group, 474 patients had thin-needle biopsy specimens taken for cytologic examination. The results of the latter examinations have been compared with those of histologic examination performed on the tissue removed during surgery. The occurrence of a malignant tumor (in 99.1%--thyroid cancer) was found in 108 patients (22.8%) from the group having thin-needle biopsy performed. Comparison of the results of cytologic examination with those of postoperative histologic examination demonstrated low sensitivity of biopsy examination (50.0%), as opposed to high specificity (96.2%) and high accuracy (85, 3%). Analysis of the false-negative results (54/108) revealed that the main causes of errors are difficulties in differentiation of adenoma from follicular carcinoma. Widening of the indications to surgery by a group of patients with adenoma will increase sensitivity to 84.8% and will require including into the operated group of about 50% of patients with scintigraphically diagnosed cold nodules: The introduction of the new term: "urgent strumectomy", has been proposed; also a diagnostic algorithm, useful for early diagnosis of malignant tumors of the thyroid, has been discussed.