OBJECTIVE: Familial risks of anxiety have been assessed in small case-control studies, usually based on reported, but not medically verified, anxiety in family members; thus the degree of familial clustering of these diseases remains to be established. METHODS: The Multigeneration Register, in which all men (sons) and women (daughters) born in Sweden from 1932 onward are registered together with their parents, was linked to hospital admission data. Standardized incidence ratios (SIRs) were calculated as the ratio of the observed to the expected number of cases of men and women with mothers and/or fathers affected by anxiety, compared with men and women whose mothers and/or fathers were not affected by anxiety. RESULTS: A total of 55,642 and 57,196 cases of anxiety were recorded in offspring and parents, respectively. The overall significant SIRs among men and women with a mother, father or both parents hospitalized for anxiety varied between 1.90 and 5.10. Maternal transmission of anxiety was slightly higher than paternal and the highest SIRs were found in the youngest age groups and among those with both parents affected by anxiety. The degree of parental transmission of anxiety was similar for both men and women. CONCLUSIONS: This study has provided the first data on age-specific familial clustering of anxiety, based on medically confirmed records. The risks were so high that hereditary factors were considered to be likely to contribute, possibly modified by environmental factors. Age-specific risks tables would be helpful for clinical counseling.