Somatostatin is a peptide with a broad distribution in the nervous system and acts as a neurotransmitter in several organs, having a wide range of mainly inhibiting effects, such as the suppression of growth hormone release, as well as the inhibition of pancreatic and gastrointestinal hormone release. Five somatostatin receptor subtypes have been cloned and demonstrated to have an emphasized expression in all human tumours. In particular, type 2 receptors were identified as the most frequently represented on the surface of neuroendocrine tumour cells, providing the molecular basis for many clinical applications of somatostatin analogues. Towards the end of the 1980s, the in vivo demonstration of somatostatin receptors on the surface of some tumours raised interest in receptor imaging, and indeed the peptide receptor overexpression on tumour cells, as compared to normal tissues, constitutes the basis for molecular imaging of these tumours. This review intends to illustrate the development of single photon emission radiopharmaceuticals for the study of somatostatin receptors and their application in diagnostic imaging.