I-131 MIBG scintigraphy was performed on a neonate who presented with a left neck mass and brachial palsy. Increased uptake of the tracer was apparent in the mass, initially suspected as being a neuroblastoma, but later diagnosed as infantile myofibromatosis. Since MIBG is principally taken up by neuroendocrine tumors, this finding suggests caution be used when interpreting studies in this age group.