We describe an accurate and simple method of diagnosing thyroid nodules by the modified technique of ultrasound-guided fine needle aspiration biopsy (UG-FNAB). An Aloka SSD 2000 focus type scanner (Aloka Co., Tokyo, Japan) equipped with a 10-MHz mechanical sector probe and a 7.5-MHz convex probe was used. First, a clear picture of the thyroid gland was taken with the use of the 10-MHz probe to determine the abnormalities. Then, a 7.5-MHz probe (1.5 x 0.8 cm of surface area) was used to guide the needle perpendicularly to the neck. This method enabled us to obtain samples from nodules greater than 5 mm. We applied this technique to 1000 patients who had uncertain diagnosis by the conventional method of FNAB. The advantages of this method are as follows: (i) The use of a small probe (7.5 MHz) is most important, since a needle can be inserted by watching the monitor without an assistant. (ii) The biopsy site can be chosen precisely. (iii) Small thyroid cancers, i.e., 5 mm cancer, can be biopsied without any difficulty. (iv) A life-threatening anaplastic carcinoma can be diagnosed at an early stage. (v) An intraglandular metastasis to the opposite lobe can be detected. (vi) Cystic carcinoma, difficult to diagnose by FNAB, can be diagnosed accurately. This method is highly recommended for all clinicians who are currently doing FNAB.