Social anxiety disorder, also known as social phobia, is one of the most prevalent anxiety disorders, affecting 7-13% of subjects in the community at some time in their lives. Despite being eminently treatable, it remains largely under-recognised and, therefore, undertreated. The disorder is characterized by a fear of scrutiny by others, with sufferers experiencing excessive anxiety in social and performance situations. This excessive anxiety usually leads to avoidance behaviour that can severely affect normal daily living. With onset commonly occurring during childhood or adolescence, social anxiety disorder may disrupt normal patterns of development of social and personal relationships, often having a long-term impact on emotional stability in social or working life. If left untreated, the course of social anxiety disorder is frequently complicated with comorbid conditions, particularly major depression or substance abuse. This review assesses the size of the clinical problem by evaluating current and lifetime prevalence estimates, age of onset, risk factors and evolution of the clinical course; thereby providing the rationale for early recognition and prompt treatment.