To investigate the utility of thallium 201 (Tl-201) thyroid scintigraphy for the detection of thyroid malignancies, early and delayed Tl-201 scintigraphy was done in 70 consecutive patients with a clinically solitary cold (Iodine 123 [I-123]) nodule. Early Tl-201 scintigraphy had a sensitivity of 100% and a specificity of 7% in predicting malignancy. With a combination of early and delayed Tl-201 scintigraphy, sensitivity ranged from 17 to 25% and specificity from 95 to 100%. Early and and delayed Tl-201 scintigraphy are only of limited value for the detection of thyroid cancer.