The authors review current understanding of generalized anxiety disorder, with particular regard to the clinical description made by the DSM-III-R. Discussion is focused on the validity of the diagnostic criteria of the disorder and on the debate on the nosological position of the illness. The review cites evidence regarding prevalence of the disorder and data on its comorbidity with the other anxiety disorders and with mood disorders. Evidence on intra-episodic, longitudinal and familial co-morbidities are assessed. Aspects of psychopathology of generalized anxiety disorders are also discussed.