Adolescence and young adulthood is a time of rapid development. Although many people successfully negotiate this period, some do not. In this paper the evidence for the treatment of some of the most important adolescent psychological problems is considered. The problem areas of depression, anxiety disorders, conduct disorders, attention deficit hyperactivity disorder, eating disorders, alcohol and substance abuse disorders, suicide, and psychotic disorders are considered in turn. After reviewing these different areas of adolescent psychological dysfunction, guidelines for clinicians are offered. The literature review also provides the opportunity to clarify areas that future research could investigate. It is suggested that a closer link between research and clinical practice will ensure improved effectiveness of treatments provided to adolescents and the development of an evidence base for treatment in early adulthood.