Publisher Summary This chapter discusses neuropeptides in neuroblastomas and ganglioneuromas. Neuroblastoma and ganglioneuroma are neural crest-derived childhood tumours that produce various neuropeptides. These peptides cause symptoms and influence tumor growth and differentiation. Analyzing neuropeptides in tissue and plasma may be useful for diagnosing, characterizing, and monitoring patients with these tumors and further indicate novel therapeutic modalities. The identification of specific neuropeptide receptors on tumor cells provides novel means for tumor imaging in vivo and innovative therapy. Several neuropeptides are produced and released by neuroblastoma and ganglioneuroma tumors, and may be significant with regard to symptoms, and growth or differentiation of tumour cells. These peptides may provide clinically useful markers and indicate novel therapeutic options in these patients. Investigating these tumors and derived cell lines provide further insight into biological characteristics of neuropeptides and their receptors. Accumulating data show that neuropeptide Y is associated with neuroblastoma growth and is a useful clinical marker with prognostic significance when analyzed in plasma. Vasoactive intestinal peptide (VIP), somatostatin and pancreastatin are associated with favourable differentiated sympathetic tumors. VIP and somatostatin have been shown to play a functional role in vitro. New means of in vivo detection of tumors expressing specific receptors, such as high-affinity somatostatin receptors, provides better imaging and characterization of neuroblastoma, and better selection of patients for specific therapeutic measures.