The presence of germline and somatic mutations in the RET proto-oncogene (RET) in patients with hereditary and sporadic medullary thyroid carcinoma (MTC) may have important ramifications for patient management. It has been suggested that the presence of the mutation ATG-->ACG at codon 918 in sporadic MTC is associated with a worse prognosis, and hence the need for more aggressive surgical, or other, treatment. Since fine-needle aspiration biopsy (FNAB) is an important component of the preoperative management of patients with thyroid tumors, we developed a rapid (20-min) method that enables extraction of DNA from FNABs for RET mutation analysis. The method allows preoperative genetic analysis to aid in management of patients with MTC, and may be applied to other tumor types where a preoperative mutation analysis based on polymerase chain reaction amplification is desired.