Rectilinear scan findings were correlated with the surgically documented size, location and histology of thyroid carcinoma in 67 patients. At the site of the carcinoma, 36 (54%) had hypofunction, associated with a palpable abnormality in all but 1 patient; 16 (24%) had an abnormality on palpation but not on scanning; 11 (16%) had a normal clinical examination and a normal scan, associated with a benign abnormality in another part of the thyroid and 4 (6%) had a patchy uptake. A literature review established that use of the .gamma.-camera with pinhole collimator does not increase the specificity of carcinoma predictability, despite enhanced sensitivity. The scan may still be used in evaluating clinically solitary nodules that are not obviously malignant. Unless these nodules are hyperfunctioning, clinical criteria rather than appearance of the scan should contribute most to the decision of whether to treat surgically.