Objective. Radiological-cytopathological correlation in patients who are prediagnosed ultrasonographically as thyroiditis. Study Design. Fourty five patients with hypoechogenic, heterogeneous, and/or pseudolobulated thyroid gland sonographically were included in this prospective study. Except for the patients with subacute thyroiditis, none of the patients had a prediagnosis of thyroiditis clinically. All patients were evaluated for their thyroid gland functions and intraglandular vascularity and ultrasonography-guided fine needle aspiration biopsy (US-FNAB) was performed. Results. The diagnosis of thyroiditis was confirmed in 36 patients (16 lymphocytic thyroiditis, 20 Hashimoto thyroiditis, two subacute granulomatous thyroiditis) in sonographically suspected patients. In six patients, FNAB was thyroiditis negative. The true diagnosis ratio of thyroiditis was increased up to 81.8% (%95 Confidence Interval: 0.70-0.92) by performing US-FNAB, while it was 4.5% with only clinical and laboratory findings (p=0.0001). Conclusion. Hypoechogenic, heterogeneous thyroid gland may be strongly related to thyroiditis, which does not have any specific radiological findings. The sonographic finding of generalized parenchymal abnormality should alert the clinician to consider diffuse thyroid disease as the underlying cause and FNAB should be performed and a follow-up examination of these patients must be continued due to the risk of neoplastic disease of thyroid.