Tc-99m sestamibi, originally developed for myocardial studies, has been used as a tumor-seeking agent. Recently, the agent also was reported to be a functional tracer to predict multidrug resistance-related p-glycoprotein expression in tumor tissue. The current report presents the authors' experience with sestamibi tumor scintigraphy in a neuroblastoma. Although I-131 MIBG tumor imaging and Tc-99m MDP bone scanning accurately demonstrated the extent of the disease, Tc-99m sestamibi showed no accumulation in primary and metastatic foci. Lack of sestamibi uptake was initially thought to be suggestive of failure to respond to chemotherapy because of p-glycoprotein expression. However, the patient responded well to chemotherapy and complete remission was achieved. The failure of Tc-99m sestamibi to detect a neuroblastoma and the lack of sestamibi accumulation in the tumor may not always be related to chemotherapy resistance.