This paper examines the literature regarding preadolescent (ages 9-12) psychiatric disorders, mental health problems, substance abuse disorders and the ecology of risk and protection. The paper is divided into three primary sections. The first section addresses the challenges in defining and applying disorders for preadolescents. The next section reviews the prevalence of psychiatric disturbances and substance abuse among preadolescents. This section also examines the state of knowledge regarding the emotional problems that do not meet DSMIV criteria as disorders but that may be prodromal for future disorders. The final section reviews risks and preventive factors as well as an ecological theoretical framework that organizes the influences of psychiatric disturbances and substance use. The primary conclusion drawn from this review of the literature is that preadolescence is a critical developmental crossroads for the expression of mental health problems and the initiation of substance abuse and that researchers and clinicians should pay particular attention to this vulnerable age range.