The article considers modern approaches to the diagnostic of generalized anxiety disorder. It presents the criteria of the main mental disorders classifications—ICD-10 and DSM-IV and their interrelationship. The typical clinical features and clinical course variants are described. The main comorbid states and the most frequent somatic pathology are presented. The article emphasizes the main issues of differential diagnosis, considering the states that should be excluded. The main predictors of the lingering course of GAD are considered. Diagnostic GAD algorithm is suggested, taking into account the results of the clinical, experimental-psychological, instrumental and laboratory methods. The dignostic process steps are described.