Pegvisomant is a GH receptor antagonist (GHR) licensed for the treatment of acromegaly. The story of the development of pegvisomant began with the recognition of the therapeutic implications of GH gene transgenic mice having a dwarf, rather than giant, phenotype and culminated in studies demonstrating its ability to normalise IGF-I in up to 97% of patients. The defining studies used pegvisomant as a daily monotherapy but more recent data suggest pegvisomant can be as effective when administered as a weekly preparation or in combination with somatostatin analogues or dopamine agonists. It is well tolerated and available data do not provide any evidence of potentiation of tumour growth. Approximately 3% of patients experience elevation in liver transaminases, typically within weeks of commencing treatment. The aetiology remains uncertain and available data suggest that it resolves on discontinuation of the drug. Important long term safety and efficacy data will continue to be provided by the ACROSTUDY registry that is open to all patients receiving pegvisomant.