Psychiatric comorbidity between anxiety disorders and substance-related disorders is studied. This relationship is complex due to the overlapping of symptoms (during the abstinence of alcohol and opiates as well as in the intoxication of cocaine) and also for the inaccurate definition of several disorders. Epidemiologic studies show an increase of prevalence of anxiety disorders, mainly agoraphobia and social phobia, in patients who are alcohol dependents and in heroine and cocaine users. Such studies also point out an augmentation of consume of substances (drugs and alcohol), with a prevalence of 24% in patients with several anxiety disorders. The relationship between these disorders is analysed. It is also studied the influence of such a comorbidity in the evolution and outcome of treatment.