Although use of the term "theranostic" is relatively recent, the concept goes back to the earliest days of nuclear medicine, with the use of radioiodine for diagnosis and therapy of benign and malignant thyroid disease being arguably the most successful molecular radiotherapy in history. A diagnostic scan with <sup>123</sup>I-, <sup>124</sup>I-, or a low activity of <sup>131</sup>I-iodide is followed by therapy with high activity <sup>131</sup>I-iodide. Similarly, adrenergic tumours such as phaeochromocytoma and neuroblastoma can be imaged with <sup>123</sup>I-metaiodobenzylguanidine and treated with <sup>131</sup>I-metaiodobenzylguanidine. Bone scintigraphy can be used to select patients with painful bone metastases from prostate cancer who may benefit from treatment with beta- or alpha-particle emitting bone seeking agents, the most recent and successful of which is <sup>223</sup>Ra radium chloride. Anti-CD20 monoclonal antibodies can be used to image and treat non-Hodgkins lymphoma, though this has not been as commercially successful as initially predicted. More recently established theranostics include somatostatin receptor targeting peptides for diagnosis and treatment of neuroendocrine tumours with agents such as <sup>68</sup>Ga-DOTATATE and <sup>177</sup>Lu-DOTATATE, respectively. Finally, agents which target prostate-specific membrane antigen are becoming increasingly widely available, despite the current lack of a commercial product. With the recent licensing of the somatostatin peptides and the rapid adoption of <sup>68</sup>Ga- and <sup>177</sup>Lu-labelled prostate-specific membrane antigen targeting agents, we have built upon the experience of radioiodine and are already seeing a great expansion in the availability of widely accepted theranostic radiopharmaceuticals.