The introduction of highly sensitive imaging techniques has made it possible to detect many nonpalpable thyroid nodules (non-PTN). We investigated the value of ultrasound-guided fine-needle aspiration biopsy (US-guided FNAB) as a diagnostic tool in the management of non-PTN as well as palpable thyroid nodules (PTN) that were considered difficult to aspirate without guidance. US-guided FNAB was performed on a total of 119 nodules (71 palpable and 48 nonpalpable) from 119 patients between 1992 and 1996. All available clinical and follow-up data were reviewed. Surgical follow-up was available in 24 cases. The patients included 100 females and 19 males ranging in age from 9 to 81 years (average, 51 years). FNA diagnoses (PTN versus non-PTN) included papillary carcinoma (12.7% [9/71] versus 4.2% [2/48], follicular neoplasm (16.9% [12/71] versus 0%), medullary carcinoma (1.4% [1/71] versus 0%), atypical cytology (5.6% [4/71] versus 2.1% [1/48], non-neoplastic thyroid (63.4% [45/71] versus 85.4% [41/48]) and unsatisfactory (0% versus 8.3% [4/48]). In 2 cases of occult papillary carcinoma, risk factors included radiation exposure (1 case) and a newly developed nodule during follow-up for hypothyroidism (1 case). Subsequent surgical follow-up (24 cases) confirmed the FNA findings, except for a case of Hürthle cell adenoma and 1 of Hashimoto's thyroiditis diagnosed as papillary carcinoma and follicular neoplasm, respectively. US-guided FNAB in most non-PTN are diagnosed as benign. For most patients with non-PTN and without any high-risk factors, a conservative approach such as clinical follow-up may be a more cost effective and logical approach. In contrast, US-guided FNAB is more useful in diagnosing biologically significant lesions in PTN that may be difficult to aspirate without guidance.