"If you have a son who does nothing good… deliver him at once into the hands of a merchant who will send him to another country... Nothing else can be done. While he remains with you, he will not mend his ways.” So wrote Florentine merchant Paolo of Certaldo in the 14th century. Teenagers have long frustrated adults with apparent black and white thinking, egocentric thoughts, irrational behaviour and focus on the present. But can raging hormones account for such behaviour and is the teenage brain really an immature structure? In this lecture we will explore some truths and myths regarding the adolescent brain, considering brain development and changes from childhood through adolescence to adulthood. We will examine the effects of alcohol, nicotine and cannabis on the teen brain, together with teenage mental health issues. We will conclude by offering a defence of the adolescent brain!