Gynaecomastia is the proliferation of the male breast glandular tissue and should be distinguished from lipomastia (weight-related fat deposition, also known as pseudogynaecomastia). The development of subareolar ductular tissue and fibrosis in gynaecomastia produces a firmer consistency compared to adipose tissue, which can be differentiated on examination. Gynaecomastia is common and can affect up to two-thirds of adult men. Typically, gynaecomastia arises from an imbalance between the oestrogenic and androgenic effects on the male breast tissue; i.e. due to deficient androgen levels (absolute or relative) or excess oestrogen levels. Whilst it is usually a benign condition, exclusion of serious conditions is important. Benign causes include secondary to certain medications, chronic kidney or liver disease. In addition, hypogonadism (primary or secondary to pituitary disease) or hyperthyroidism, are important common endocrine aetiological causes. Having excluded these causes of gynaecomastia, it is imperative to be vigilant for underlying malignancy causing gynaecomastia. These include oestrogen secreting testicular tumours, oestrogen secreting feminising adrenal tumours and human chorionic gonadotrophin secreting testicular and extra testicular tumours. A careful history and physical examination with simple biochemical testing is adequate for most patients. However, patients with elevated serum oestradiol or human chronionic gonadotrophin (hCG) concentrations require radiological investigations to exclude testicular, adrenal and other extra testicular tumours.