Breast accumulation of I-131 may be an undesirable effect of I-131 ablation in postpartum women being treated for differentiated thyroid cancer. The use of diagnostic I-123 scintigraphy before ablation does allow an assessment of potential postablative breast uptake in such patients. This case series of 8 patients evaluates I-123 scintigraphy in the assessment of breast uptake in postpartum women with thyroid cancer. Of these patients, 7 were studied at various times after cessation of lactation and in one patient, lactation was not initiated at all. Of the group who did not receive lactation-inhibiting medications, there was variable breast uptake demonstrated and by 6 months postcessation of lactation, some patients showed persisting breast uptake but others demonstrated no uptake. In the group treated with lactation-inhibiting medications, such as bromocriptine or cabergoline, breast uptake appears to be reduced much earlier with uptake becoming absent after as little as 3 weeks of treatment. There was barely discernible uptake in the patient in whom lactation was never initiated. I-123 scintigraphy may help guide clinicians on the appropriate timing of radioiodine ablation to help minimize concentration of I-131 in breast tissue.