Over a three-month period in 2012, we saw four boys aged between 14 and 15 with attention deficit hyperactivity disorder (ADHD) in clinic with delayed puberty. Only one boy was on medication to treat his ADHD, while the mother of another said, ‘I thought he was delayed because of his ADHD’. This led us to ask ourselves whether there was a documented link between ADHD and delayed puberty. Delayed puberty is generally defined as a lack of secondary sexual characteristics from the age of 14 in boys and 13 in girls. In boys, this includes the absence of testicular development (testicular volume less than 4 ml) and, in girls, a lack of breast development. Most of the theories around whether ADHD is associated with delayed puberty focus on the use of stimulant medication. On the website Healthy Children (www.healthychildren.org), Dr Norman Spack states that a side-effect of the use of stimulant medication in ADHD is suppressed appetite, which, in turn, may lead to pubertal delay, either indirectly initiated or aggravated by the fact that the children are not consuming enough calories. A study to examine whether methylphenidate damaged DNA found, as an incidental finding, that high doses of the drug reduced the size of the testes and delayed the descent of testes in male monkeys younger than five years old, compared with monkeys not given the drug. The drug also reduced their testosterone levels at both low and high doses. However, the effects were not permanent.