Agoraphobia is believed to run in families, but this belief is not well supported by the literature. Data were gathered on the risk of agoraphobia in parents and siblings of 60 agoraphobic probands; 12 1/2% of the relatives were reported to have or have had agoraphobia. This risk is significantly greater than estimates of the population incidence, and requires explanation. The details of the pedigrees do not directly support simple genetic models while investigations into environmental factors in agoraphobia by other workers have been inconclusive. As a putative case has been established for the familial occurrence of agoraphobia, further work is required to shed light on whether genetic or cultural factors are paramount.