Studying comorbidity may be particularly useful in shedding light on the nature, course, and management of generalized anxiety disorder (GAD). This article reviews the common comorbidities in GAD, their impact on functioning and on medical utilization, and their implications for treatment. Comorbidity in this area is complex in that GAD may be primary (predating other illnesses) or secondary (following other conditions). Nevertheless, studies demonstrate the high prevalence of patients with a matrix of anxious-somatic-depressive symptoms and show that GAD comorbidity is associated with both increased disability and increased medical utilization. Clinical implications of this work include the need for rigorous assessment of anxiety, somatic, and depressive symptoms in patients who present with any one of these sets of complaints and the possibility that early treatment of GAD may be critical in preventing subsequent morbidity.