Radioiodinated metaiodobenzylguanidine [131I-MIBG] is commonly used to treat resistant neuroblastoma or metastatic pheochromocytoma [MP] with little non-hematopoietic toxicity. We describe here transient sialoadenitis, a previously unreported complication. Ten patients [9 neuroblastoma and 1 MP] received 12–18 mCi/kg of 131I-MIBG. Five patients had bilateral parotid swelling, two with associated buccal discomfort within 24 hr of injection which subsided within 48 hr. Grade 3 or 4 serum amylase elevation was documented in 8/8 patients tested [median 1,336; range: 576–8,830 U/L] which normalized [25–125 U/L] within 4–14 [median 5.5] days. Serum lipase remained normal. Patients did not develop subsequent dry mouth or dysphagia. Pediatr Blood Cancer 2008;50:1271–1273. © 2007 Wiley-Liss, Inc.