Precocious puberty may be suspected when secondary sexual characteristics appear in a girl younger than 8 years or a boy younger than 9 years. It may lead to accelerated skeletal development and a reduction in final adult height. It can have a significant psychosocial and physical impact for children and their parents. Most patients do not require extensive investigations, although a sinister underlying causes such as a tumour should always be considered and excluded. Idiopathic (or true) precocious puberty is common in girls. It is rare in boys, therefore it is more important to investigate and find a cause in boys.