The lifetime prevalence of anxiety disorders was estimated in a study of the prevalence of mental disorders in Iceland. The survey instrument was an Icelandic translation of the US National Institute of Mental Health Diagnostic Interview Schedule. The cohort consisted of one half of those born in the year 1931. The participation rate was 79.3%. The overall prevalence of anxiety disorders was 44%, with phobia effecting 18%. The most common anxiety disorder was generalized anxiety, which had a prevalence of 22% and was more common among women. Simple phobia was the most common of the phobic disorders (8.8%), followed by agoraphobia without panic (3.8%), and social phobia (3.5%). The female-male ratio for anxiety disorders was 2:1. Of those with simple phobia, the most common items were a fear of heights (41%); claustrophobia (34%); being on public transportation (31%); the fear of being in crowds and speaking in front of others (28%); of being alone (24%); of insects (22%); of bad weather (21%); and of being in water (aquaphobia) (20%). In addition, 17% of the respondents listed phobias not cited in the DSM-III, and of those with the most common phobic disorder, only 9% had consulted a physician because of this condition. Post-traumatic stress disorder was found to affect women exclusively. Comorbidity shows a mean of at least 3 additional diagnoses.