The article describes a follow-up of 595 fine needle aspiration cytology samples of the thyroid gland taken during the five-year periode 1983-87. Of these samples, 133 (22.4%) were unsatisfactory for diagnosis. Among the remaining samples there were seven false negative and two false positive diagnoses of cancer. The false negative diagnoses were due to inadequate cytologic material not representative of the malignant tumor. The false positive diagnoses were due to cytomorphologic misinterpretation.