[en] For routine thyroid scanning, the sodium pertechnetate Tc-99m scan is preferred over sodium iodide I-131 scanning in many laboratories. Radiation safety for the patient and reduction of costs are the primary reasons for this. Discrepancies can occur between iodine scans (iodine I-123 and ¹³¹I) as compared with /sup 99m/Tc scans: e.g., a nodule appearing cold on an iodine scan may be warm with a /sup 99m/Tc scan. To give other examples of discrepancies that can occur when /sup 99m/Tc is compared with iodine, we present two cases