Fine-needle aspiration cytology (FNAC) is the reference diagnostic tool in patients with thyroid nodules. Because the true diagnosis is based on histopathologic findings, the final diagnosis of nodules not operated on is postponed, impacting the cost. We aimed to determine the cost of FNAC by taking account of diagnostic mistakes, failures, and follow-up of patients who did not have surgery.A Markov model described the management of patients according to initial cytopathologic results. Estimates for accuracy values and follow-up were derived from a retrospective study of 624 patients. Costs were computed from the hospital perspective. Sensitivity analyses were performed. Of the lesions, 381 were cytopathologically classified as benign, 15 as malignant, 57 as "suspicious," and 171 as unsatisfactory. The cost of diagnosis was 1,145 euros . Cost was significantly affected by the unsatisfactory specimen percentage (27.4%), without which the cost would be reduced by 35.5%, to euros 738. Cost depends on cytopathologist performance and the unsatisfactory rate. In the future, routine ultrasound guidance and on-site assessment of cytopathologic adequacy would help reduce costs.